Composite material, reactor, converter, and power conversion device

ABSTRACT

There is provided a composite material containing magnetic powder and a polymeric material including the powder in a dispersion state, wherein a content of the magnetic powder with respect to the whole composite material is more than 50% by volume and 75% by volume or less, a saturation magnetic flux density of the composite material is 0.6 T or more, and a relative magnetic permeability of the composite material is more than 20 and is 35 or less. It is preferable that a density ratio of the magnetic powder should be 0.38 or more and 0.65 or less. The density ratio is set to be an apparent density/a true density. Moreover, it is preferable that the magnetic powder should include a plurality of particles constituted of the same material.

TECHNICAL FIELD

The present invention relates to a composite material suitable as amaterial constituting a magnetic part such as a reactor or the like, areactor including a magnetic core formed of the composite material, aconverter including the reactor, and a power conversion device includingthe converter. In particular, the present invention relates to a reactorcapable of reducing a loss and having a small number of components, anda composite material which is suitable for the reactor.

BACKGROUND ART

A magnetic part including a coil and a magnetic core having the coildisposed thereon, for example, a reactor or a motor is used in variousfields. For example, Patent Literature 1 discloses a reactor used as acircuit component of a converter or the like mounted on a vehicle suchas a hybrid electric vehicle. Patent Literature 1 discloses, as amaterial constituting the magnetic core provided in the reactor, acomposite material constituted of magnetic powder such as pure ironpowder and a resin (binder) containing the powder. The compositematerial can be manufactured by filling a molding die of a desirableshape or the like with a mixture obtained by mixing magnetic powder andan uncured liquid resin which are raw materials, and then curing theresin.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent No. 4,692,768

SUMMARY OF INVENTION Technical Problem

It is desirable that a loss should be small as a desired characteristicfor the magnetic core. From a viewpoint of productivity of a magneticpart such as a reactor, moreover, it is desirable that the number ofcomponents should be small. Accordingly, it is desirable that themagnetic core should include the small number of components.

According to Patent Literature 1, a gap is not provided by constitutingthe magnetic core using the composite material. Thus, a gap material canbe omitted and the number of components can be reduced. In PatentLiterature 1, the composite material is set to have a relative magneticpermeability of 11 or less in order to prevent a gap from beingprovided. Since the relative magnetic permeability is low, thus, thereis a possibility that a magnetic flux might leak, resulting in a lossdue to the leakage of the magnetic flux.

Therefore, an object of the present invention is to provide a reactorcapable of reducing a loss and having a small number of components.Moreover, another object of the present invention is to provide acomposite material which is suitable for building the reactor.

Still another object of the present invention is to provide a converterincluding the reactor and a power conversion device including theconverter.

Solution to Problem

The present invention particularly achieves the object by setting therelative magnetic permeability of the composite material into a specificrange.

The composite material according to the present invention containsmagnetic powder and a polymeric material including the powder in adispersion state, and a content of the magnetic powder with respect tothe whole composite material is more than 50% by volume and 75% byvolume or less, a saturation magnetic flux density of the compositematerial is 0.6 T or more, and a relative magnetic permeability of thecomposite material is more than 20 and 35 or less. A method of measuringthe saturation magnetic flux density and the relative magneticpermeability will be described in a test example which will be explainedlater.

Since the composite material according to the present invention has therelative magnetic permeability of 35 or less which is comparatively low,magnetic flux saturation occurs with difficulty. For this reason, it ispossible to reduce a gap material and an air gap, and more preferably,to omit the gap material or the like by using the composite materialaccording to the present invention in a magnetic core of a magnetic partsuch as a reactor. Accordingly, it is possible to contribute toreduction in the number of components for the magnetic part such as thereactor. Moreover, the composite material according to the presentinvention has the relative magnetic permeability which is more than 20.In the case where the composite material is used for the magnetic coreof the magnetic part such as the reactor, therefore, a magnetic fluxcreated by a coil leaks with difficulty. By using the composite materialaccording to the present invention in the magnetic core of the magneticpart such as the reactor, therefore, it is possible to reduce a loss andto contribute to reduction in the loss in the magnetic part such as thereactor. Furthermore, the composite material according to the presentinvention has the content of the magnetic powder which is which is morethan 50 volume %. For this reason, the proportion of a magneticcomponent is sufficiently high. Therefore, the composite materialaccording to the present invention can have a saturation magnetic fluxdensity which is enhanced and is 0.6 T or more. Since the content of themagnetic powder is 75% by volume or less, in manufacture, a mixturecontaining the magnetic powder and a polymeric material which are rawmaterials of the composite material can easily flow so that compositematerials having various shapes can be formed with high precision.Accordingly, the composite material according to the present inventionis also excellent in productivity. Moreover, the composite materialaccording to the present invention is also excellent in form accuracyand dimensional precision.

In the case where the material of the magnetic powder has a saturationmagnetic flux density of approximately 2 T (for example, pure iron, aFe—Si alloy or the like), particularly, the content of the magneticpowder is more than 50% by volume so that the saturation magnetic fluxdensity of the composite material is easily set to be 1.0 T or more. Inthis case, if the content of the magnetic powder is 55% by volume ormore, the saturation magnetic flux density of the composite material isset to be 1.1 T or more. It is more preferable that the content of themagnetic powder in the composite material should be 55% by volume ormore and 70% by volume or less.

There may be an aspect of the composite material according to thepresent invention, in which a density ratio of the magnetic powder is0.38 or more and 0.65 or less. The density ratio is set to be anapparent density/true density. The apparent density is obtained based onJIS Z 2504 (2000) “Metallic powders—Determination of apparent density”.The true density indicates a density at which only a volume occupied bya substance is set to be a density calculating volume. In the case wherean inner part of each particle constituting the magnetic powder has nocavity, the true density is equal to a specific gravity of a material(for example, a metal such as pure iron) constituting the magneticpowder.

The composite material according to the aspect can be manufactured byutilizing, in the raw material, magnetic powder satisfying a densityratio which is 0.38 or more and 0.65 or less, for example. By using thespecific raw material, it is possible to manufacture the compositematerial according to the present invention which satisfies a specificrelative magnetic permeability and a specific saturation magnetic fluxdensity without applying a high pressure in molding. According to theaspect, therefore, productivity is excellent. By using powder having ahigh apparent density within a range satisfying the density ratio,moreover, it is possible to raise a packing density. By using powderhaving an apparent density satisfying the density ratio of 0.65 or less,furthermore, it is possible to suppress an electrical connection througha contact of the particles of the magnetic powder as greatly aspossible, thereby suppressing the relative magnetic permeability of thecomposite material at a low value. As a result, it is possible toimplement a comparatively low relative magnetic permeability whilesetting a comparatively high saturation magnetic flux density.

There may be an aspect of the composite material according to thepresent invention, in which the magnetic powder includes a plurality ofparticles constituted of the same material.

The magnetic powder is constituted of a particle of a single material.Therefore, it is sufficient that one type of magnetic powder is used asthe raw material of the composite material.

There may be an aspect of the composite material according to thepresent invention, in which the magnetic powder is constituted of thesingle material, the magnetic powder is iron powder and an apparentdensity of the iron powder is 3.0 g/m³ or more and 5.0 g/cm³ or less.

The pure iron has a higher saturation magnetic flux density than a Fe—Sialloy or the like. For this reason, in the aspect, the saturationmagnetic flux density is apt to be increased. Moreover, the pure ironhas a true density of 7.874 g/cm³. For this reason, in the case wherethe apparent density of the pure iron satisfies the range, the ironpowder satisfies the density ratio which is 0.38 or more and 0.65 orless. According to the aspect, therefore, the saturation magnetic fluxdensity is high, and furthermore, the composite material tends to have arelative magnetic permeability which is more than 20 and 35 or less asdescribed above, and productivity is also excellent.

There may be an aspect of the composite material according to thepresent invention, in which the magnetic powder contains powderconstituted of a plurality of materials having different relativemagnetic permeabilities from each other. If the composition of themagnetic substance differs, the relative magnetic permeability isusually varied. In the aspect, accordingly, the relative magneticpermeability is used as an index of the difference between thecompositions of the magnetic substance.

In the aspect, there are contained magnetic powder formed of a pluralityof materials having different relative magnetic permeabilities from eachother, that is, magnetic powder having a high relative magneticpermeability and magnetic powder having a comparatively low relativemagnetic permeability. Therefore, it is possible to have characteristicsof the respective powder together. More specifically, the magneticsubstance having the high relative magnetic permeability typically has ahigh saturation magnetic flux density, and furthermore, the magneticsubstance having the low magnetic permeability typically has a highelectric resistivity. Therefore, it is possible to reduce an eddycurrent loss. In the aspect, accordingly, the high saturation magneticflux density and the low loss can be more easily compatible with eachother as compared with the case where magnetic powder formed of a singlematerial is contained. In the aspect in which the magnetic substancehaving the low relative magnetic permeability is contained, moreover, asaturation of a magnetic flux occurs with difficulty. For this reason, agap member or the like can further be reduced easily. In addition, inthe case where a composite material having a high saturation magneticflux density and a low loss is manufactured, the eddy current loss canbe reduced but it is not necessary to use very fine magnetic powderwhich is hard to handle, and the saturation magnetic flux density can beenhanced. However, it is not necessary to increase the content of themagnetic powder with reduction in viscosity of a mixture of rawmaterials. Therefore, the aspect is also excellent in productivity.

There may be an aspect of the composite material according to thepresent invention, in which there is a plurality of peaks when aparticle size distribution of the magnetic powder is taken.

The peak takes a frequency f_(s) of a particle diameter r_(s) which isless than a particle diameter r_(x) by a predetermined value k (k is adesign value) and a frequency f_(L), of a particle diameter r_(L) whichis more than the particle diameter r_(x) by the predetermined value k (kis the design value), the frequency f_(x) being 1.1 times or more asgreat as the frequency f_(s) and being 1.1 times or more as great as thefrequency f_(L) when having the frequency f_(x) of the particle diameterr_(x) having a particle size distribution.

The composite material according to the present invention can bemanufactured by mixing magnetic powder and a polymeric material such asa resin or rubber which are raw materials to prepare a mixture, fillinga predetermined molding die with the mixture and then curing thepolymeric material. By the manufacturing method, a shape or a diameterof a particle of the magnetic powder used for the raw material is notchanged substantially before and after the manufacture. For this reason,the particle size distribution of the magnetic powder in the compositematerial is substantially equal to that of the magnetic powder used forthe raw material.

The presence of a plurality of peaks in the particle size distributionindicates that a peak (a high frequency value) is present in a pointhaving a small particle diameter and a point having a large particlesize in a histogram of the particle size distribution. In other words,at least two peaks: a first peak and a second peak are present, and whena particle size having the first peak is represented by r₁ and aparticle size having the second peak is represented by r₂, a particlediameter r₁ is less than a particle diameter r₂ (r₁<r₂). The aspect inwhich the plurality of peaks is present includes both fine magneticpowder and coarse magnetic powder at a high frequency. By including thefine magnetic powder in a comparatively large amount, the aspect canreduce an eddy current loss, resulting in a small loss. By using mixedpowder containing the fine powder and the coarse powder for the rawmaterial, moreover, it is possible to easily enhance a packing densityof the magnetic powder. Consequently, it is possible to obtain acomposite material having a high proportion of a magnetic component. Inthe aspect, accordingly, the saturation magnetic flux density is high.Furthermore, it is possible to easily enhance the packing density byutilizing the mixed powder. For this reason, it is not necessary to useonly very fine powder which is hard to handle. Thus, it is possible toutilize powder having such a size as to be easily handled. In theaspect, therefore, the magnetic powder to be used for the raw materialis easily handled and the productivity is also high. In addition, withthe use of the mixed powder for the raw material, the mixture with thepolymeric material has fluidity enhanced. For this reason, even acomposite material having a complicated shape can be molded with highprecision. In this respect, the aspect is excellent in the productivity.In the aspect, the saturation magnetic flux density is enhanced if themagnetic powder is constituted of a single material and the singlematerial is pure iron, and the eddy current loss can be reduced if thesingle material is an iron alloy.

In addition, the presence of the peaks in the particle size distributionis determined whether the peaks are present in the whole magnetic powderor not regardless of the number of the materials of the magnetic powder.More specifically, the following cases are included.

(A) Magnetic powder such as pure iron or an iron alloy is constituted ofa single material, and a plurality of peaks is seen in the particle sizedistribution.

(B) Magnetic powder constituted of different types of materials, forexample, pure iron and an iron alloy are included, and a single peak isseen in a particle size distribution of a certain material (for example,the pure iron) and a single peak is seen in a particle size distributionof another material (for example, the iron alloy). However, particlessizes to be mutual peaks are shifted from each other.

(C) The magnetic powder constituted of different types of materials, forexample, pure iron and an iron alloy are included and a plurality ofpeaks is seen in each of particle size distributions of a certainmaterial (for example, pure iron) and the other material (for example,an iron alloy). In this case, the peaks for the certain material (forexample, the pure iron) and the peaks for the other material (forexample, the iron alloy) may overlap with each other or may be shiftedfrom each other.

(D) The magnetic powder formed of different types of materials, forexample, iron pure and an iron alloy are included, and a single peak isseen in a particle size distribution for a certain material (forexample, the pure iron) and a plurality of peaks is seen in a particlesize distribution for the other material (for example, the iron alloy).In this case, the single peak for the certain material (for example, thepure iron) and the single peak for the other material (for example, theiron alloy) may overlap with each other or may be shifted from eachother.

There may be an aspect of the composite material according to thepresent invention, in which a degree of circularity of a particleconstituting the magnetic powder is 0.1 or more and 2.0 or less. Amethod of measuring the degree of circularity will be described later.

For example, the composite material according to the aspect can bemanufactured by utilizing, for a raw material, the magnetic powderconstituted of the particle satisfying the specific degree ofcircularity. The magnetic powder is excellent in fluidity, andfurthermore, can fully form a clearance in which another particle can beinterposed between the particles satisfying the specific degree ofcircularity. By using the specific raw material, accordingly, it ispossible to easily enhance the packing density of the magnetic powder.The composite material thus obtained has a high proportion of a magneticcomponent and a high saturation magnetic flux density. From theforegoing, in the aspect, a composite material having a high saturationmagnetic flux density can easily be obtained, and furthermore,productivity is also high. The degree of circularity is preferably 1.0or more and 1.5 or less, and is further preferably 1.0 or more and 1.3or less.

The composite material according to the present invention can besuitably utilized for a magnetic core of a magnetic part, for example, amagnetic core of a reactor provided in a converter or the like which isto be mounted on a vehicle such as a hybrid electric vehicle. As thereactor according to the present invention, therefore, there is proposeda reactor which includes a coil and a magnetic core and has at least apart of the magnetic core constituted of the composite materialaccording to the present invention.

The reactor according to the present invention has at least a part ofthe magnetic core which is constituted of the composite materialaccording to the present invention. Consequently, it is possible toproduce special advantages. More specifically, (1) a gap member or thelike can be reduced, and preferably, can be omitted so that the numberof the components is small, (2) a magnetic flux created by a coil ishard to leak to an outside of the magnetic core so that a loss can bereduced, (3) it is possible to include a magnetic core having asaturation magnetic flux density of 0.6 T or more, and (4) magneticcores having various shapes can be manufactured with high precision, andproductivity is also high.

As the reactor according to the present invention, alternatively, thereis proposed a reactor which includes a coil and a magnetic core and hasthe whole magnetic core constituted of the composite material accordingto the present invention.

The reactor also produces the advantages (1) to (4) described above. Inparticular, a relative magnetic permeability of the whole magnetic coreis more than 20 and 35 or less. Therefore, the gap member or the likecan further be reduced, and preferably, can be omitted. In manufactureof the magnetic core, moreover, it is sufficient to manufacture only thecomposite material. As compared with the case where a magnetic coreincluding a powder compact or the like in combination is manufactured, amanufacturing process can be simplified. Accordingly, the rectoraccording to the aspect can further reduce the number of the componentsand enhance the productivity.

The reactor according to the present invention can be suitably utilizedfor the component of the converter. As the converter according to thepresent invention, therefore, a converter including the reactoraccording to the present invention is proposed.

If the converter according to the present invention includes the reactoraccording to the present invention which has a small number ofcomponents and can reduce a loss, the productivity is high and a lowloss is obtained.

The converter according to the present invention can be suitablyutilized for the component of the power conversion device including aconverter and an inverter. As the power conversion device according tothe present invention, therefore, a power conversion device includingthe converter according to the present invention is proposed.

If the power conversion device according to the present inventionincludes, as a component, the reactor according to the present inventionwhich has a small number of components and can reduce a loss, theproductivity is high and a low loss is obtained.

Advantageous Effects of Invention

The reactor according to the present invention includes a small numberof components and can reduce a loss. The composite material according tothe present invention can build a magnetic core of the reactor whichincludes a small number of components and can reduce a loss.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1(A) is a brief perspective view showing a reactor according to afirst embodiment and FIG. 1(B) is a cross-sectional view showing thereactor taken along line B-B.

FIG. 2 is a perspective view showing an assembly of a coil and an innercore which are provided in the reactor according to the firstembodiment.

FIG. 3(A) is a brief perspective view showing a reactor according to athird embodiment and FIG. 3(B) is a brief perspective view showing amagnetic core provided in the reactor.

FIG. 4 is a brief structure diagram schematically showing a power supplysystem of a hybrid electric vehicle.

FIG. 5 is a brief circuit diagram showing an example of a powerconversion device according to the present invention including aconverter according to the present invention.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present invention will be specifically describedbelow with reference to the drawings. Like reference signs refer to likemembers in the drawings.

First Embodiment

With reference to FIGS. 1(A), 1(B), and 2, a reactor 1 according to afirst embodiment will be described. The reactor 1 includes a singlecylindrical coil 2 obtained by spirally winding a wire 2 w, and amagnetic core 3 disposed on an inside and an outside of the coil 2 andforming a closed magnetic circuit. In this example, an assembly of thecoil 2 and the magnetic core 3 is accommodated in a case 4. A feature ofthe reactor 1 is a component of the magnetic core 3. More specifically,at least a part of a portion disposed on the inside of the coil 2 in themagnetic core 3 is made of a powder compact, and at least a part of aportion disposed on the outside of the coil 2 is made of a specificcomposite material. The magnetic core 3 will be described below indetail and subsequently the other components will be described.

[Magnetic Core]

The magnetic core 3 is a member for forming paths of a magnetic fluxwhen the coil 2 is energized. As shown in FIG. 1(B), the magnetic core 3according to this example includes a columnar inner core 31 having atleast a part disposed on the inside of the coil 2 and covered with thecoil 2, and an outer core 32 disposed on the outside of the coil 2 andformed to substantially cover a part of the inner core 31 and acylindrical outer peripheral surface of the coil 2. A materialconstituting the inner core 31 and a material constituting the outercore 32 are different from each other. More specifically, the inner core31 is made of a powder compact and the outer core 32 is constituted of acomposite material containing magnetic powder and a polymeric materialincluding the powder in a dispersion state. In the reactor 1, one offeatures is that the composite material has a relative magneticpermeability which is more than 20 and 35 or less.

{Inner Core}

The inner core 31 according to this example is a columnar member alongwith an inner peripheral shape of the cylindrical coil 2. It is possibleto properly select sectional and external shapes of the inner core 31.For example, the inner core 31 may have a prism shape such as arectangular-parallelepiped shape, an ellipsoid shape, or the like andmay have a similar shape to an inner peripheral shape of the coil 2, andfurthermore, a non-similar shape. The inner core 31 according to thisexample is assumed to be a solid element in which neither a gap membersuch as an alumina plate nor an air gap is interposed.

When a length in an axial direction of the coil 2 (a vertical directionin FIG. 1(B)) is referred to as a length of the inner core 31 or alength of the coil 2, the length of the inner core 31 according to thisexample is greater than the length of the coil 2 shown in FIG. 1(B).Moreover, the inner core 31 is accommodated in the case 4 such that oneend surface (a surface disposed on an opening side of the case 4 in FIG.1(B)) is almost flush with an end surface of the coil 2 and the otherend surface (a surface disposed on a bottom surface side of the case 4in FIG. 1(B)) and a vicinity thereof is protruded more than the otherend surface of the coil 2. Regarding the reactor 1, accordingly, in themagnetic core 3, a portion disposed on the inside of the cylindricalcoil 2 is formed of a powder compact constituting a part of the innercore 31, and a portion disposed on the outside of the coil 2 is formedof a powder compact constituting the other part of the inner core 31 anda composite material constituting the outer core 32.

It is possible to properly select a protrusion length of the inner core31. Herein, there is employed a configuration in which only the otherend surface side of the inner core 31 is protruded more than the otherend surface of the coil 2. However, it is also possible to employ aconfiguration in which each end surface of the inner core 31 isprotruded more than each end surface of the coil 2. At this time, it isalso possible to employ any configurations in which the protrusionlengths are equal to each other or different from each other.Alternatively, it is possible to employ a configuration in which thelength of the inner core 31 and that of the coil 2 are equal to eachother, that is, a configuration in which each end surface of the innercore 31 and that of the coil 2 are flush with each other. For example,it is possible to employ a configuration in which in the magnetic core3, only a portion disposed on the inside of the coil 2 is made of apowder compact, and a whole portion disposed on the outside of the coil2 is made of a composite material. All of the configurations describedabove include the composite material such that a closed magnetic circuitis formed when the coil 2 is energized.

The powder compact can typically be obtained by molding and then burningmagnetic powder constituted of a magnetic particle, coating magneticpowder including a magnetic particle and an insulating coating formed ona surface thereof, and mixed powder having a binder mixed properly inaddition to these powder. In the case where the coating magnetic powderis used for a raw material, the burning is carried out at aheat-resistance temperature of the insulating coating or less. Examplesof the insulating coating in the coating magnetic powder of the rawmaterial include a phosphate compound, a silicone resin and the like.The insulating coating in the raw material remains intact after theburning in some cases and is changed into a compound which will bedescribed later or the like by the burning in the other cases. Byregulating a material of the magnetic particle, a mixture ratio of themagnetic powder and the binder, and amounts of various coatingscontaining the insulating coating, and adjusting a molding pressure inthe manufacture of the powder compact, it is possible to change amagnetic characteristic of the powder compact. For example, whenmagnetic powder constituted of a material having a high saturationmagnetic flux density is used, a blending amount of the binder isreduced to enhance a proportion of a magnetic component, or a moldingpressure is raised, a powder compact having a high saturation magneticflux density is obtained. The powder compact can easily be molded evenwhen it is in a relatively complicated three-dimensional shape, and thushigh productivity is exhibited.

Examples of the material of the magnetic particle include an iron-basematerial, for example, an iron group metal such as Fe, Co or Ni (pureiron made of Fe and inevitable impurities, for instance), an iron alloycontaining Fe as a principal component (a Fe—Si based alloy, a Fe—Nibased alloy, a Fe—Al based alloy, a Fe—Co based alloy, a Fe—Cr basedalloy, a Fe—Si—Al based alloy or the like), a rare earth metal alloy,and a soft magnetic material such as ferrite to be an iron oxide. Inparticular, with the iron-base material, it is easier to obtain a powdercompact having a higher saturation magnetic flux density than theferrite. Examples of a material constituting an insulating coatingformed at the powder compact include a phosphate compound, a silicacompound, a zirconium compound, an aluminum compound, a boron compoundand the like. Examples of the binder include a thermoplastic resin, anon-thermoplastic resin, higher fatty acid and the like. The binder maydisappear due to the burning described above or may change into aninsulator such as silica. In connection with the powder compact, aninsulator such as an insulating coating is present between the magneticparticles so that the magnetic particles are insulated from each other.Accordingly, even in the case where the coil is energized withhigh-frequency power, an eddy current loss is small. In the case wherethe magnetic particle is formed of a metal, the insulating coating canreduce the eddy current loss if any. In the case where the magneticparticle is formed of an insulator such as ferrite, the insulatingcoating does not need to be included. It is possible to utilize thepowder compact which is well known.

It is possible to properly select a saturation magnetic flux density ora relative magnetic permeability of the inner core 31. In the case wherea constant magnetic flux is to be obtained, it is possible to decreaseat least a sectional area of a portion covered with the coil 2 (an areaof a portion through which a magnetic flux passes) as an absolute valueof the saturation magnetic flux density in at least a portion coveredwith the coil 2 in the inner core 31 is greater and the saturationmagnetic flux density of at least the portion covered with the coil 2 inthe inner core 31 is relatively more than that of the outer core 32. Forthis reason, it is possible to reduce a size of the reactor 1 having ahigh saturation magnetic flux density of the inner core 31 (it ispossible to decrease a volume thereof). Accordingly, it is preferablethat the saturation magnetic flux density of at least the portioncovered with the coil 2 in the inner core 31 should be 1.6 T or more,should further be 1.8 T or more and should particularly be 2 T or more,and should be at least 1.2 times or more as great as the saturationmagnetic flux density of the outer core 32, should further be at least1.5 times or more as great as that, and should particularly be at least1.8 times or more as great as that, all of which have no upper limit.When a lamination product of electromagnetic steel sheets represented bya silicon steel sheet is utilized for the material constituting theinner core 31 in place of the powder compact, the saturation fluxdensity of the inner core 31 can easily be further enhanced.

Herein, the powder compact constituting the inner core 31 is formed ofsoft magnetic metal powder including a coating such as an insulatingcoating, and has a magnetic flux density which is 1.6 T or more and arelative magnetic permeability which is 100 or more and 500 or less.

[Outer Core]

The outer core 32 according to this example is a solid element which isprovided to generally cover the outer periphery of an assembly (FIG. 2)of the coil 2 and the inner core 31 and in which neither a gap membernor an air gap is interposed. In detail, the outer core 32 is formed tocover both end surfaces and an outer peripheral surface in the coil 2,and one end surface and an outer peripheral surface on the other endsurface side in the inner core 31, and as shown in FIG. 1(B), itscross-sectional shape taken along the axial direction of the coil 2 isan inverted U-shape. The outer core 32 and a part of the inner core 31are bonded to each other by a polymeric material in the outer core 32 toform a closed magnetic circuit, and furthermore, to configure theintegral magnetic core 3. In other words, the magnetic core 3 accordingto this example does not have another member such as an adhesiveinterposed between the inner core 31 and the outer core 32.

The outer core 32 can have any shape if the closed magnetic circuit canbe formed. For example, it is possible to employ a configuration inwhich a part of the outer periphery of the coil 2 is not covered withthe composite material constituting the outer core 32. Referring to ahorizontal configuration which will be described later (a fifthembodiment), it is possible to easily manufacture a configuration inwhich a part of the outer periphery of the coil 2 is exposed from thecomposite material.

Magnetic Powder

Examples of the material of the magnetic powder in the compositematerial include the iron base material such as an iron group metal, forexample, pure iron or an iron alloy, a metal such as a rare earth metalalloy, and a soft magnetic material such as a compound (a nonmetal), forexample, ferrite. The magnetic powder constituting the compositematerial may be of the same type as the magnetic powder of the powdercompact constituting the inner core 31 or may contain powder formed ofdifferent types of materials.

An exemplary pure iron may be pure iron containing Fe in 99.5% by massor more and inevitable impurities in a residual part. The pure iron hasa high saturation magnetic flux density. For this reason, a compositematerial containing pure iron powder tends to have a saturation magneticflux density increased with a rise in a content proportion of the pureiron powder. By utilizing the composite material, it is possible toeasily obtain a magnetic core having a high saturation magnetic fluxdensity. For example, it is possible to employ a composite material inwhich magnetic powder contains the largest amount of pure iron powder ora composite material in which all of magnetic powder is constituted ofpure iron powder.

Herein, magnetic powder can contain coating powder including a magneticparticle and an insulating coating covering an outer periphery of themagnetic particle. In a composite material containing the coatingpowder, the insulating coating is interposed between the magneticparticles and the magnetic particles can be insulated from each other.For this reason, the composite material containing the coating powdercan easily reduce an eddy current loss. By utilizing the compositematerial, it is possible to readily obtain a magnetic core having a lowloss. As a content proportion of the coating powder in the magneticpowder is increased, the eddy current loss can be reduced so that amagnetic core having a low loss can easily be obtained. Examples of aninsulating material constituting the insulating coating includephosphate, a silicone resin, metal oxide, metal nitride, metal carbide,a metal phosphate compound, a metal borate compound, a metal silicatecompound and the like. Examples of a metal element included in theoxide, a compound such as a metal salt compound include Fe, Al, Ca, Mn,Zn, Mg, V, Cr, Y, Ba, Sr, a rare earth element (excluding Y) and thelike. The listed material is a nonmagnetic material and includes aninsulating coating constituted of the nonmagnetic material, therebysuppressing an increase in a relative magnetic permeability. It ispreferable that pure iron powder should be the coating powder becausethe eddy current loss can be reduced as described above. If iron allypowder which will be described below is set to be the coating powder,the eddy current loss can be reduced more easily, and furthermore, therelative magnetic permeability can readily be decreased.

Examples of the iron alloy include an alloy containing at least oneelement selected from Si, Ni, Al, Co and Cr as an additive element in anamount which is 1.0% by mass or more and 20.0% by mass or less in total.More specifically, examples of the iron alloy include a Fe—Si basedalloy, a Fe—Ni based alloy, a Fe—Al based alloy, a Fe—Co based alloy, aFe—Cr based alloy, a Fe—Si—Al based alloy and the like. The iron alloygenerally has a higher electric resistance than the pure iron. Inparticular, the iron alloy containing Si, for example the Fe—Si basedalloy or the Fe—Si—Al based alloy (Sendust) has a high electricresistivity. For this reason, the composite material containing the ironalloy powder can reduce an eddy current loss, and furthermore, has asmall hysteresis loss. By utilizing the composite material, it ispossible to easily obtain a magnetic core having a low loss. Forexample, it is possible to obtain a composite material in which allmagnetic powder is constituted of iron alloy powder (preferably, ironalloy powder containing Si). In some cases in which the compositematerial contains iron alloy powder having different compositions, asaturation magnetic flux density is enhanced in addition to thereduction in the eddy current loss.

The magnetic powder in the composite material may be constituted of thesingle material (only the pure iron powder or the like) as describedabove. Alternatively, the magnetic powder in the composite material cancontain powder constituted of a plurality of materials having differentrelative magnetic permeabilities. For example, there are employed aconfiguration including pure iron powder and iron alloy powder and aconfiguration including iron alloy powder having a plurality ofdifferent compositions. In the former configuration, the saturationmagnetic flux density can be enhanced by containing the pure iron powderand the eddy current loss can be reduced by containing the iron alloypowder. By utilizing the composite material, accordingly, it is possibleto easily obtain a magnetic core having a high saturation magnetic fluxdensity and a low loss. In this configuration, as a content of the pureiron powder is increased, the saturation magnetic flux density can beenhanced. For this reason, in the case where an enhancement in thesaturation magnetic flux density is desired, the magnetic powderpreferably contains the pure iron powder in the largest amount, and morepreferably contains the majority of the pure iron powder. In the latterconfiguration, all of the magnetic powder is the iron alloy powder.Therefore, the eddy current loss can be reduced. By utilizing thecomposite material, it is possible to easily obtain a magnetic corehaving a low loss. By regulating the composition of the iron alloy, itis also possible to enhance the saturation magnetic flux density.

A particle constituting the magnetic powder may have an optional shapesuch as a spherical shape and a non-spherical shape (for example, aplate shape, a needle shape, a rod shape or the like, other differentshapes). The magnetic powder used in the raw material as described aboveand the magnetic powder in the composite material have shapes or sizeswhich are substantially equal to each other. By using magnetic powderhaving a desirable particle shape in the raw material, therefore, it ispossible to obtain a composite material containing the magnetic powderhaving the desirable particle shape (in which a degree of circularity tobe described later satisfies a specific range, for example).

If the shape of the particle constituting the magnetic powder is closeto the spherical shape, a clearance in which another particle(preferably, a finer particle than the particle) can be interposed tendsto be formed in a clearance between the spherical particles. As aresult, the packing density of the magnetic powder tends to be enhanced.By enhancing the packing density, the composite material having the highsaturation magnetic flux density as described above can easily beobtained. When the particle constituting the magnetic powder has thespherical shape, moreover, there is a tendency that the loss of thecomposite material is small. With the increase in the number of portionswhere the magnetic particles dispersed into the composite material comein contact with each other, the relative magnetic permeability of thecomposite material is excessively increased or an eddy current flowsinto a portion between the magnetic particles if the particles areformed of a metal. For this reason, there is a fear that the loss mightbe increased. Even if the spherical particles are adjacent to eachother, however, the spherical particles simply come in point contactwith each other substantially and rarely come in face contact with eachother. Accordingly, it is supposed that the loss can be reduced. In themanufacture of the composite material, therefore, it is proposed toutilize, for the raw material, a particle constituting the magneticpowder which has a degree of circularity of 1.0 or more and 2.0 or less.

The degree of circularity is set to be a maximum diameter/circleequivalent diameter. The circle equivalent diameter specifies a contourof the particle constituting the magnetic powder and is a diameter of acircle having the same area as an area S surrounded by the contour. Inother words, the circle equivalent diameter is represented by a circleequivalent diameter=2×{an area S/π in the contour}^(1/2). The maximumdiameter is set to be a maximum length of the particle having thecontour. For example, the area S is obtained by fabricating a sample inwhich the magnetic powder to be used for the raw material is hardenedwith a resin or the like and observing a section of the sample using anoptical microscope, a scanning type electron microscope: SEM or thelike. It is sufficient to cause the observed image of the section thusobtained to be subjected to image processing (for example, binarizationprocessing) or the like, thereby extracting the contour of the particleto calculate the area S in the contour. Referring to the maximumdiameter, a maximum diameter of the particle is extracted from thecontour of the particle which is extracted. In the case where the SEM isutilized, a measuring condition includes the number of sections: 50 ormore (one visual field per section), a magnification: 50 to 1000, thenumber of particles to be measured per visual field: 10 or more, and thetotal number of particles: 1000 or more.

A particle having the degree of circularity of 1 which is measured asdescribed above corresponds to a perfect sphere. As the degree ofcircularity of the magnetic powder used in the raw material approximatesto 1, it is possible to obtain an enhancement in packing density and anachievement of excellent flowability. As the degree of circularity ofthe magnetic powder in the composite material approximates to 1, it ispossible to reduce the loss and suppress an excessive increase in therelative magnetic permeability. Accordingly, it is preferable that thedegree of circularity should be 1.0 or more and 1.5 or less, andparticularly, should be 1.0 or more and 1.3 or less.

As described above, in order to increase the relative magneticpermeability through the excessive contact of the particles and toreduce the generation and increase of the eddy current, particularly ifthe particle is formed of a metal, it is desirable that the magneticpowder should be the coating powder. In the case where the powder havingthe particle shape approximating the perfect sphere having a degree ofcircularity satisfying a specific range is used for the raw material,even the magnetic particle having no insulating coating can suppress theexcessive contact of the particles, thereby reducing the relativemagnetic permeability of the composite material. Accordingly, the use,for the raw material, of the magnetic powder having the degree ofcircularity satisfying the specific range is taken as one of effectivestructures for manufacturing a composite material in a saturationmagnetic flux density having a great value of 0.6 T or more, andfurthermore, 1.0 T or more, and at the same time, a relative magneticpermeability having a comparatively small value of 35 or less.

In order to manufacture powder having the degree of circularitysatisfying the specific range, for example, powder is fabricated by agas atomizing method using an inert gas for a cooling medium or powderhaving different shapes formed by a water atomizing method or the like(powder having a degree of circularity out of the specific range) issubjected to round processing such as grinding. In the case where thegrinding is carried out, it is possible to regulate a degree ofcircularity of magnetic powder to be used in a raw material by properlyselecting a particle size of an abrasive grain. However, a method ofobtaining powder having a predetermined degree of circularity is notrestricted to these methods but it is sufficient to manufacture powderby the method of obtaining the degree of circularity. Also in some casesin which the magnetic powder to be used for the raw material containscoarse powder, moreover, the loss of the composite material is reducedwith powder having a shape approximating a spherical shape, that is,powder having a degree of circularity which approximates to 1.0. Thecomposite material is formed at a comparatively low pressure so that adegree of circularity of each particle constituting the magnetic powderin the composite material is substantially equal to a degree ofcircularity of each particle constituting the magnetic powder used forthe raw material (the degree of circularity satisfies 1.0 or more and2.0 or less). In order to measure the degree of circularity of themagnetic powder in the composite material, for example, the section ofthe composite material is taken and an image observed by microscopeobservation for the section is used as described above.

In the case where magnetic powder having a specific particle sizedistribution which will be described later is used for the raw material,a packing density can be enhanced effectively even if the particles hasa nonspherical shape. Consequently, it is possible to obtain a compositematerial having a high proportion of a magnetic component. In otherwords, in the case where the particle size distribution of the magneticpowder to be used for the raw material is regulated, powder having anoptional particle shape can be utilized for the raw material in themanufacture of the composite material. Therefore, the particle shape ofthe magnetic powder which can be used for the raw material has a highdegree of freedom.

A size of the magnetic particle in the composite material can beselected properly. For example, the particle size of the magneticparticle is 10 μm or more and 200 μm or less. Moreover, the magneticparticle in the composite material can contain various particles havingdifferent sizes from each other. For example, when the particle sizedistribution of the magnetic particle in the composite material istaken, it can take a configuration in which a plurality of peaks ispresent. In brief, a certain particle having a small particle size and acertain particle having a large particle size are present at a highfrequency to some degree. According to this configuration, fineparticles can be interposed in a clearance formed between coarseparticles. For this reason, the composite material has a high saturationmagnetic flux density because the packing density of the magnetic powdercan easily be enhanced and the proportion of the magnetic componenttends to be raised. In addition, as the particle size of the magneticpowder is smaller, the eddy current loss can be reduced. Therefore, thecomposite material containing fine particles has a low loss.

The number of the peaks may be two or three or more. When magneticpowder having a particle size distribution with only one peak (forexample, powder with a broad peak, powder with a steep peak or the like)is used for the raw material, the raw material is hard to handle andworkability is reduced if the magnetic powder is fine, and the packingdensity is reduced if the magnetic powder is coarse. On the other hand,if two peaks are present depending on the particle size, the reductionin the workability can be suppressed, and furthermore, the packingdensity can be enhanced fully. In other words, when a particle sizehaving a first peak and a particle size having a second peak in theparticle size distribution are represented by r₁ and r₂ respectively, itis sufficient that two peaks satisfying r₁<r₂ are present. In the caseof a configuration in which two peaks satisfying r₁≦(½)×r₂ are present,particularly, a fine particle having the particle diameter r₁ to be ahalf of the coarse particle having the particle diameter r₂ or less canbe fully interposed in the clearance between the coarse particles sothat the packing density can be enhanced. Accordingly, the saturationmagnetic flux density is enhanced, and furthermore, the fine particle ispresent at a high frequency. Consequently, it is possible to obtain acomposite material having a low loss. As a difference between theparticle sizes r₁ and r₂: r₂−r₁ is increased, the clearance isefficiently filled with the fine particle so that the packing densitytends to be enhanced. Accordingly, it is preferable that the particlediameter r₁ should satisfy r₁≦(⅓)×r₂. If the particle diameter r₁ isexcessively small, however, handling is hard to perform so thatworkability tends to be reduced. For this reason, it is preferable thatr₁≧( 1/10)×r₂ should be satisfied. Regardless of the material, as theparticle diameter r₁ is smaller, a loss (particularly, an eddy currentloss or an iron loss), cab be reduced and as the particle diameter r₁ islarger, the magnetic powder is easier to handle.

It is possible to employ a configuration in which the magnetic powderhaving the plurality of peaks is constituted of a material of the sametype (the same composition), that is, a configuration in which themagnetic powder is constituted of a single material or a configurationin which the magnetic powder is constituted of a plurality of materialsof different types. In the case of the former single material, forexample, when the magnetic powder is pure iron powder, the particlediameter r₁ is 50 μm or more and 100 μm or less and the particlediameter r₂ is 100 μm or more and 200 μm or less, and preferably, theparticle diameter r₁ is 50 μm or more and 70 μm or less and the particlediameter r₂ is 100 μm or more and 150 μm or less (where, r₁<r₂,preferably r₁≦(½)×r₂). The composite material contains, at a highfrequency, a sufficiently large particle having the particle diameter r₂satisfying the range with respect to a fine particle having the particlediameter r₁ satisfying the range. Consequently, the difference betweenthe particle diameter r₁ and the particle diameter r₂ is great so thatthe packing density can easily be enhanced. For this reason, theproportion of the magnetic component in the composite material becomesgreater so that the saturation magnetic flux density is enhanced. Sincethe magnetic powder is the pure iron powder, the composite material hasthe higher saturation magnetic flux density. Moreover, the compositematerial contains, at a high frequency, the sufficiently fine particle(the particle having the particle diameter r₁) which is 50 μm or moreand 100 μm or less with respect to the particle diameter r₂.Consequently, the eddy current loss can be reduced. Since the particlediameter r₂ is 200 μm or less, the eddy current loss can easily bereduced so that the composite material has a low loss. Furthermore, aparticle size of the finest particle present at a high frequency is 50μm or more. Therefore, the number of very fine particles having particlesizes of less than 50 μm is small so that the iron powder to be used forthe raw material can easily be handled and workability is excellent.

In the case of the former single material, for example, when themagnetic powder is iron alloy powder, it is possible to employ aconfiguration in which handling can easily be carried out in theparticle size of 50 μm or less and the particle diameter r₁ satisfies 50μm or less. For example, it is possible to employ a configuration inwhich the particle diameter r₁ is 10 μm or more and 40 μm or less. It ispossible to employ the particle diameter r₂ which is 40 μm or more and150 μm or less (where, r₁<r₂). According to this configuration, theparticle diameter r₁ is smaller and the magnetic powder is constitutedof an iron alloy. Therefore, it is possible to produce advantages of (1)the eddy current loss is further reduced so that a composite materialhaving a low loss can be obtained, and (2) since the packing density caneasily be further enhanced, the saturation magnetic flux density is alsohigh to some degree although the magnetic powder is constituted of theiron alloy. Moreover, a comparatively fine iron alloy having a particlediameter of 50 μm or less can form a spherical particle more easily andis also excellent in productivity of fine and spherical powder.

In the case of the latter materials of different types, for example, itis possible to employ a configuration in which a plurality of peaks ispresent when the particle size distribution of the magnetic powder istaken, and at least two of the peaks are peaks of the powder constitutedof materials having different relative magnetic permeabilities from eachother. Referring to this configuration, both the fine magnetic powderand the coarse magnetic powder are contained at a high frequency and thematerials of the individual pieces of powder are different from eachother. Referring to this configuration, the magnetic powder constitutedof the different materials is contained. Based on the composition,consequently, it is possible to enhance the saturation magnetic fluxdensity or to reduce the eddy current loss. Referring to thisconfiguration, furthermore, the fine and coarse mixed powder iscontained. Therefore, a high packing density can be obtained.Accordingly, the saturation magnetic flux density is high. As a morespecific configuration, for example, it is possible to employ aconfiguration in which one of peaks is a peak of pure iron powder andthe other peak is a peak of iron alloy powder, a configuration in whichthe respective peaks are peaks of the iron alloy powder having differentcompositions from each other.

In the configuration including the pure iron powder and the iron alloypowder, in the case where powder having any of the peaks which has thesmallest particle size is the pure iron powder, that is, the case wherethe pure iron powder has the particle diameter r₁ and the iron alloypowder has the particle diameter r₂, the fine pure iron powder isincluded at a high frequency. Even if the pure iron powder is contained,therefore, the eddy current loss can be reduced. Referring to thisconfiguration, therefore, a high saturation magnetic flux density can beobtained by the pure iron powder at a high frequency, and the fine pureiron powder and the iron alloy powder are mixed so that a low loss canbe acquired. Referring to this configuration, moreover, a fine pure ironparticle having a high saturation magnetic flux density tends to becontinuously present around the coarse iron alloy particle. For thisreason, a magnetic flux can easily pass uniformly. As a specificparticle size according to this configuration, the particle diameter r₁is 50 μm or more and 100 μm or less, and furthermore, is 50 μm or moreand 70 μm or less. The particle diameter r₂ is 50 μm or more and 200 μmor less (where, r₁<r₂), and furthermore, is 150 μm or less.

In the configuration including the pure iron powder and the iron alloypowder, in the case where the powder having any of the peaks which hasthe smallest particle size is the iron alloy powder, that is, the casewhere the iron alloy powder has the particle diameter r₁ and the pureiron powder has the particle diameter r₂, the fine iron alloy powder isincluded at a high frequency. Consequently, the eddy current loss can bereduced more greatly. Referring to this configuration, therefore, a highsaturation magnetic flux density can be obtained by containing the pureiron powder, and the low loss can further be obtained by containing thefine iron alloy powder. As a specific particle size according to thisconfiguration, the particle diameter r₁ is 50 μm or less, andfurthermore, is 10 μm or more and 30 μm or less. The particle diameterr₂ is 100 μm or more and 200 μm or less, and furthermore, is 140 μm ormore and 200 μm or less (preferably, r₁≦(½)×r₂).

Referring to a configuration including only the iron alloy powder, it ispossible to employ a configuration having a higher saturation magneticflux density or a configuration having a lower loss depending on thecharacteristic of the powder having any of the peaks which has thesmallest particle diameter, for example. As a specific particle sizeaccording to this configuration, the particle diameter r₁ is 50 μm orless, and furthermore, is 10 μm or more and 30 μm or less. The particlediameter r₂ is 30 μm or more and 200 μm or less (where, r₁<r₂), andfurthermore, is 40 μm or more and 150 μm or less.

In order to measure the particle size distribution of the magneticpowder in the composite material, for example, a polymer component isremoved to extract the magnetic powder, and the magnetic powder thusobtained is analyzed by using a particle size analyzer. This techniquecan measure the particle size distribution of the magnetic powder withhigh precision because the polymer component is not present. In the casewhere the magnetic powder constituted of a plurality of differentmaterials is contained, the particle size distribution may be measuredevery composition of the magnetic powder and these particle sizedistributions may be then synthesized. In the case where the compositematerial contains nonmagnetic powder which will be descried later, it ispreferable to select the magnetic powder and the nonmagnetic powder bymeans of a magnet, for example. Alternatively, X-ray diffraction, energydispersion X-ray spectroscopy: EDX or the like may be utilized to carryout component analysis, thereby performing the selection. A commerciallyavailable particle size analyzer can be utilized.

In order to manufacture the composite material having the particle sizedistribution described above, there is utilized magnetic powdercontaining, at high frequencies, particles having particle diameters r₁₀and r₂₀ satisfying r₁₀<r₂₀ (preferably, r₁₀≦(½)×r₂₀) in the raw materialrespectively. In the case where commercially available powder is used,it is sufficient to check the particle size distribution, therebyutilizing powder satisfying the specific particle size distribution. Inorder to satisfy a desirable particle diameter, classification may becarried out by using a sieve or the like. The magnetic powder to be usedfor the raw material can be manufactured typically by using an atomizingmethod (a gas atomizing method, a water atomizing method or the like).By utilizing the powder manufactured through the gas atomizing method,particularly, there is a tendency that a composite material having asmall loss is obtained. It is also possible to obtain a desirableparticle diameter by properly grinding coarse powder. By preparingplural powder having different particle diameters as described above andutilizing the powder satisfying the degree of circularity for the rawmaterial, moreover, it is possible to easily obtain a composite materialhaving a lower loss and a higher saturation magnetic flux density.

By using, for the raw material, magnetic powder having a smalldifference in the particle diameter, the particle size distribution ofthe magnetic powder in the composite material may have only one peak. Inthe case where magnetic powder having the same particle sizedistribution and a different composition is used for the raw material,moreover, the particle size distribution of the magnetic powder in thecomposite material has only one broad peak or steep peak.

There is included magnetic powder in the composite material satisfying adensity ratio=an apparent density/a true density which is 0.38 or moreand 0.65 or less. This composite material can be manufactured by using,for the raw material, the magnetic powder having a density ratio whichis 0.38 or more and 0.65 or less. The density ratio of the magneticpowder in the composite material thus obtained substantially maintainsthe density ratio of the magnetic powder used in the raw material. Byusing, for the raw material, the magnetic powder having the densityratio of 0.38 or more, it is possible to manufacture a compositematerial having a saturation magnetic flux density of 0.6 T or morewithout excessively raising a pressure in molding. The magnetic powderhaving the density ratio of 0.65 or less can easily be manufactured, andfurthermore, can be prevented from becoming deposited in a mixture,thereby performing separation when it is mixed with the polymericmaterial. Consequently, it is possible to manufacture a compositematerial having the magnetic powder disposed uniformly therein. If thedensity ratio of the magnetic powder in the composite material is 0.65or less, moreover, the relative magnetic permeability can be suppressedat a low value. Accordingly, it is possible to produce excellentadvantages that the composite material having the density ratiosatisfying the specific range (1) is excellent in the productivity ofthe raw material and the composite material, (2) is homogeneous, and (3)can reduce relative magnetic permeability.

The density ratio is 0.45 or more and is further preferably 0.5 or more,and is preferably 0.6 or less. In order to set the density ratio to be0.38 or more and be 0.65 or less, for example, powder (spherical powder)having the degree of circularity satisfying the specific range is usedfor the raw material. Accordingly, it is possible to suitably utilize,for the raw material, the powder manufactured by the gas atomizingmethod or the like as described above. By removing the coarse particleswhose contact areas are increased readily through the classification ofthe magnetic powder to be used for the raw material or the like, it ispossible to easily increase the apparent density.

In the case where the magnetic powder is the iron powder, it ispreferable that the apparent density of the iron powder should be 3.0g/cm³ or more and 5.0 g/cm³ or less. In the case where the apparentdensity of the iron powder satisfies the range, the density ratio can be0.38 or more and 0.65 or less. Accordingly, this configuration canproduce advantages that (4) the saturation magnetic flux density isenhanced by containing the pure iron powder in addition to theadvantages of (1) high productivity, (2) homogeneous and (3) a lowerrelative magnetic permeability as described above. The apparent densityof the iron powder can be changed by regulation of the particle diameteror shape of the iron powder. There is a tendency that the apparentdensity is increased as the particle size of the iron powder is smalleror the shape of the iron powder approximates to the spherical shape.

When the magnetic powder to be used for the raw material is subjected toproper surface processing in advance, it is possible to expect anadvantage that condensation can be prevented and sedimentation into apolymeric material (particularly, a resin) can be suppressed. Forexample, when the surface processing is previously carried out by asilane coupling agent or the like, adhesion between the magnetic powderand the polymeric material can be improved so that it is possible tosuppress the sedimentation of the magnetic powder in the polymericmaterial which is not hardened. For example, when the surface processingis previously carried out by a surface active agent or the like, thecondensation can be prevented. These surface processing may be carriedout sequentially or simultaneously. In mixture of the magnetic powderand the polymeric material, it is also possible to mix a surfaceprocessing agent for preventing the sedimentation. However, there is atendency that a high sedimentation preventing advantage can be obtainedby execution of the surface processing before mixture.

The content of the magnetic powder in the composite material (a totalamount regardless of a material) is set to be more than 50% by volumeand 75% by volume or less with respect to the whole composite material.The content of the magnetic powder is more than 50% by volume so thatthe proportion of the magnetic component is sufficiently high.Consequently, it is possible to obtain a composite material in which thesaturation magnetic flux density is high and the relative magneticpermeability is not excessively high but is more than 20 and 35 or less.Since the content of the magnetic powder is 75% by volume or less, themixture of the magnetic powder and the unhardened polymeric materialwhich are raw materials is excellent in fluidity in the manufacture ofthe composite material. Therefore, a molding die can be filled with themixture well. Accordingly, even a composite material having acomplicated shape can be molded with high precision so that theproductivity of the composite material is high. Moreover, the compositematerial is excellent in shape precision and dimensional accuracy. Inparticular, it is desirable that the content of the magnetic powdershould be 55% by volume or more and be 70% by volume or less. The rawmaterial is prepared to have a desirable content. The content of themagnetic powder in the composite material is obtained by removing thepolymer component to acquire a volume of the magnetic component orperforming image processing over the photomicrograph of the section toconvert a volume rate from an area rate of the magnetic component in thesection.

In the case where the content of the magnetic powder is enhanced withinthe range, for example, the case where the content is set to be 60% byvolume or more, and furthermore, be 65% by volume or more, it ispossible to easily achieve a high packing density by using the mixedpowder of the fine powder and the coarse powder as described above. Thecomposite material thus obtained has a high proportion of the magneticcomponent and a high saturation magnetic flux density.

Polymeric Material

A polymeric material to be a binder in a composite material includes aresin and rubber. Examples of the resin include a thermosetting resinsuch as a silicone resin, an epoxy resin, a phenol resin, an unsaturatedpolyester resin or a urethane resin, a thermoplastic resin such as apolyphenylene sulfide (PPS) resin, a polyamide resin, a polyimide resinor a fluororesin, and the like. It is also possible to utilize BMC (BulkMolding Compound) containing the unsaturated polyester resin as aprincipal component and a reinforcing material such as a glass fiber.Examples of the rubber include silicone rubber, fluororubber and thelike. The silicone resin, the epoxy resin, the PPS resin, the siliconerubber and the like in the listed materials are excellent in a heatresistance. In the case where the thermosetting resin or the rubber isused, a mixture filled in the molding die is heated to a predeterminedtemperature and is thus hardened. Examples of other polymeric materialsinclude a normal temperature curable resin or a low temperature curableresin. In this case, the mixture filled in the molding die is left at anormal temperature to a comparatively low temperature to cure the resin.

The composite material generally has more polymeric materials such as aresin or rubber which is a nonmagnetic material as compared with thepowder compound. Also in the case where the same magnetic powder as thepowder compact constituting the inner core 31 is contained, accordingly,the outer core 32 constituted of the composite material tends to have alower saturation magnetic flux density and a lower relative magneticpermeability than those of the powder compact. By regulating thematerial or shape of the magnetic powder, the presence or thickness ofthe insulating coating, the content of the binder or the like, it ispossible to easily change the magnetic characteristic of the compositematerial.

The composite material can be typically formed by injection molding orcast molding. The injection molding mixes the polymeric material and themagnetic powder to be the raw material in a fluidization state (a liquidstate generally having a viscosity), applies a predetermined pressure tothe mixture (a slurry-like mixture) and pours the mixture into a moldingdie having a predetermined shape to perform molding, and then hardensthe polymeric material. The cast molding obtains the same mixture asthat in the injection molding and then pours the mixture into themolding die without applying a pressure to perform molding andhardening. In the first embodiment, the case 4 can be utilized for themolding die. In this case, a composite material (in this case, the outercore 32) conforming to an inner peripheral shape of the case 4 caneasily be molded with high precision. It is also possible to fabricate aplurality of compacts having a desirable shape and combine the compactconstituted of these composite materials, thereby building the magneticcore 3 having a desirable shape.

Magnetic Characteristic

The saturation magnetic flux density of the composite material is set tobe 0.6 T or more. As the saturation magnetic flux density of thecomposite material is increased, a magnetic core having a highsaturation magnetic flux density can be built, and thus 0.8 T or more,and furthermore, 1 T or more and 1.1 T or more are preferable and anupper limit is not particularly provided. In this example, however, thesaturation magnetic flux density is set to be less than the saturationmagnetic flux density of the inner core 31 (the powder compact). In thecase where only the pure iron is used for the magnetic powder,particularly, a saturation magnetic flux density of 1.15 T or more caneasily be implemented. In the case where only the iron alloy is used forthe magnetic powder, a saturation magnetic flux density of more than1.05 T can easily be implemented.

The relative magnetic permeability of the composite material is set tobe more than 20 and 35 or less. Since the relative magnetic permeabilityof the composite material is more than 20, a loss can be reduced alsowhen the composite material is used for the magnetic core 3 (in thiscase, particularly, the outer core 32 disposed on the outside of thecoil 2). Since the relative magnetic permeability of the compositematerial is 35 or less, the magnetic core 3 is magnetically saturatedwith difficulty when the composite material is used for the magneticcore 3, and a gap member or an air gap can be reduced. As the relativemagnetic permeability of the composite material is reduced, the gapmember or the like can easily be reduced to enable contribution to thereduction in the number of the components in the reactor 1. Accordingly,it is preferable that the relative magnetic permeability of thecomposite material should be more than 20 and be 30 or less.

Herein, the composite material constituting the outer core 32 is formedof a composite material including coating powder having an insulatingcoating on a surface of a magnetic particle and an epoxy resin, andsatisfies a saturation magnetic flux density which is 0.6 T or more anda relative magnetic permeability which is more than 20 and 35 or less. Acontent of the coating powder is more than 50% by volume and 75% byvolume or less. Accordingly, the magnetic core 3 has the magneticcharacteristic which is partially different. The inner core 31 has ahigher saturation magnetic flux density than the outer core 32, and theouter core 32 has a lower relative magnetic permeability than the innercore 31. The relative magnetic permeability of the outer core 32 islower than that of the inner core 31 which is 100 or more and 500 orless. Consequently, a magnetic flux easily passes through the inner core31.

The magnetic core 3 according to this example, has a whole relativemagnetic permeability which is more than 20 and 100 or less. Themagnetic core 3 has a whole relative magnetic permeability which iscomparatively low as described above, and can wholly have an integratedgapless structure without using a gap member or an air gap.

[Coil 2]

The coil 2 is a tube-shaped member obtained by spirally winding a singlecontinuous wire 2 w. The wire 2 w is preferably a coated wire having aninsulating coating made of an insulating material on the outer peripheryof a conductor made of a conductive material such as copper, aluminum oran alloy thereof. It is possible to utilize conductors having variousshapes, for example, a rectangular wire with a rectangular crosssection, a circular wire with a circular cross section, a deformed linewith a polygonal cross section and the like. An insulating materialconstituting an insulating coating is represented by an enamel materialsuch as polyamideimide. As the insulating coating is thicker, aninsulation performance is enhanced. A specific thickness of theinsulating coating is 20 or more and 100 μm or less. The sectional areaand the winding number (the number of turns) of the wire 2 w canproperly be selected to have a desirable characteristic. The shape ofthe end surface of the coil 2 may be a shape whose an outer shape isformed solely with a curved line, for example, an annular shape shown inFIG. 2, an elliptic shape (not shown) and the like, and a flat shapewhose an outer shape is formed with a curved line and a straight line,for example, a race track shape, a corner rounded rectangular shape (seeFIG. 3 which will be described later) and the like. A cylindrical coilhaving an annular end surface is easy to wind a wire and is excellent inproductivity.

Herein, the coil 2 is an edgewise coil made of an edgewise-wound coatedrectangular wire, which includes a conductor being a copper rectangularwire with a rectangular cross-sectional shape and an insulating coatbeing enamel. The end face shape of the coil 2 has an annular shape.

An external device (not shown) such as a power supply for supplyingelectric power to the coil 2 is connected to both ends of the wire 2 wforming the coil 2. Typically, the both ends of the wire 2 w areproperly extended from a turn (are led out of the case 4 in FIGS. 1(A)and 1(B)) and a terminal member is connected to a conductor portionexposed by peeling the insulating coating, and the external device isconnected through the terminal member to the both ends of the wire 2 w.The terminal member is constituted of a conductive material such ascopper or aluminum. Welding (for example, TIG welding), contact bondingor the like is utilized for the connection of the terminal member.

The reactor 1 shown in this example employs a configuration (hereinafterreferred to as a vertical type) in which the assembly of the coil 2 andthe magnetic core 3 is accommodated such that the axial direction of thecoil 2 is orthogonal to the bottom surface of the case 4. Referring tothe vertical type, it is possible to reduce an installation area of thereactor 1 for an installation target such as a cooling table where thereactor 1 is to be installed.

[Case]

The case 4 according to this example is a rectangular parallelepipedshaped container configured with a rectangular bottom surface and fourside walls erected from the bottom surface, and has a bottomed tubeshape where a surface opposing to the bottom surface is opened. The case4 accommodates the assembly of the coil 2 and the magnetic core 3 toprotect and mechanically protect the coil 2 and the magnetic core 3 froman environment, and furthermore, is utilized for a heat-release pathwhen the reactor 1 is fixed to the installation target such as thecooling table. Accordingly, a material constituting the case 4 is amaterial having a high thermal conductivity, and preferably, a materialhaving a higher thermal conductivity than that of the magnetic powdersuch as iron. For example, it is possible to suitably utilize, as theconstituting material, a metal such as aluminum, an aluminum alloy,magnesium or a magnesium alloy. Since the aluminum, the magnesium, andthe alloy are lightweight, they are also suitable for a materialconstituting automobile components, which are desired to be lightweight.Moreover, the aluminum, the magnesium and the alloy are nonmagneticmaterials and conductive materials. For this reason, a leakage flux tothe outside of the case 4 can also be prevented effectively. Herein, thecase 4 is formed of the aluminum alloy.

In addition, the case 4 according to this example has a mount portion 41formed integrally. The mount portion 41 serves to fix the reactor 1 tothe installation target. The mount portion 41 has a bolt hole and caneasily fix the reactor 1 to the installation target by means of a bolt(not shown). If the case 4 includes a positioning portion for placingthe coil 2 or the inner core 31 into a predetermined position, moreover,it is possible to dispose the coil 2 or the inner core 31 in a properposition of the case 4. The case 4 has the positioning portion (notshown) such that the coil 2 is disposed in a central part of the case 4as shown in FIG. 1(B). If a cover constituted of a conductive materialsuch as aluminum is provided in the same manner as in the case 4,furthermore, it is possible to prevent a leakage flux and to protect ormechanically protect the outer core 32 from an environment. It ispreferable that the cover should be provided with a notch or a throughhole in order to pull out the end of the wire 2 w constituting the coil2 or a size of the cover should be regulated to form a clearance.Alternatively, it is also possible to form a cover made of a resin byseparately filling the resin in the vicinity of the opening portion ofthe case 4.

[Other Structure]

In order to enhance insulation performance between the coil 2 and themagnetic core 3, it is possible to employ a configuration in which theouter periphery of the coil 2 is covered with an insulating resin or aconfiguration in which the outer periphery of the coil 2 is covered withan insulating material such as an insulating paper, an insulating sheetor an insulating tape. Examples of the insulating resin include an epoxyresin, a urethane resin, a polyphenylene sulfide (PPS) resin, apolybutylene terephthalate (PBT) resin, an acrylonitrile butadienestyrene (ABS) resin, unsaturated polyester and the like. In order toenhance insulation performance between the coil 2 and the inner core 31,moreover, it is possible to employ a configuration in which aninsulating bobbin is provided on the outer periphery of the inner core31. The bobbin may include a tube-shaped member disposed on the outerperiphery of the inner core 31 and an annular-shaped flange portionprovided on both ends of the tube-shaped member. If the bobbin employs aconfiguration in which a plurality of divided pieces is combined to beone unit, it can easily be disposed in the inner core 31. Example of amaterial constituting the bobbin include a PPS resin, a liquid crystalpolymer (LCP), a polytetrafluoroethylene (PTFE) resin and the like. Inaddition, the outer periphery of the inner core 31 can be covered withan insulating tube such as a heat-shrinkable tube. In the case where thecoil 2 comes in contact with the case 4, furthermore, an insulatingmaterial can be interposed between the coil 2 and the case 4 in order toenhance insulation performance therebetween. When a contact portion withthe magnetic core 3 in a leading place of the wire 2 w is also coveredwith the insulating resin, the insulating material, the heat-shrinkabletube or the like, the insulation performance can be enhanced.

Alternatively, the case 4 can be omitted. By omitting the case, it ispossible to reduce the size and weight of the reactor. In the case wherethe outer peripheral surface of the assembly including the coil 2 andthe magnetic core 3 is constituted of a composite material as in thisexample, a polymer component such as a resin is contained. Also in aconfiguration in which the magnetic core 3 is exposed, therefore, it ispossible to protect and mechanically protect the coil 2 from an externalenvironment. In a configuration in which the outer periphery of theassembly including the coil 2 and the magnetic core 3 is further coveredwith the insulating resin, it is possible to protect (to enhance acorrosion resistance or the like) and mechanically protect both the coil2 and the magnetic core 3 from the external environment. If theinsulating resin contains, for example, a filler made of ceramics havinga high thermal conductivity or the like, heat-release performance ishigh, which is preferable. Moreover, the mount portion may be moldedintegrally with the portion covered with the resin.

[Purpose of Use]

The reactor 1 having the above-described structure can be preferablyutilized for a purpose of use under electricity application conditionsin which a maximum current (direct current) is in a range fromapproximately 100 to 1000 A, an average voltage is in a range fromapproximately 100 to 1000 V, and a usable frequency is in a range fromapproximately 5 to 100 kHz, or typically, a component of an on-vehiclepower conversion device in a vehicle such as an electric vehicle, ahybrid electric vehicle, etc

[Method of Manufacturing Reactor]

The reactor 1 can be manufactured in the following manner, for example.First of all, the coil 2 and the inner core 31 formed of a powdercompact are prepared and the inner core 31 is inserted into the coil 2to fabricate the assembly of the coil 2 and the inner core 31 as shownin FIG. 2. Then, the assembly is accommodated in the case 4.

A mixture of the magnetic powder and the polymeric material (unhardened)constituting the outer core 32 (FIGS. 1(A) and 1(B)) is prepared. Theyare sufficiently mixed such that the magnetic powder is uniformlydispersed, and thereafter, the mixture thus obtained is poured into themolding die (herein, the case 4). Since this mixture is excellent in thefluidity as described above, it can be filled with high precision intothe case 4 serving as a complicated molding space by the presence of thecoil 2 and the inner core 31. After the filling, the polymeric materialof the mixture is hardened so that the outer core 32 constituted of thecomposite material can be formed. Herein, the outer core 32 is formed tocome in contact with one end surface of the inner core 31 and an outerperipheral surface on the other end surface side of the inner core 31 asshown in FIG. 1(B). Consequently, it is possible to provide the magneticcore 3 forming a closed magnetic circuit when the coil 2 is energized.In this example, accordingly, the reactor 1 is obtained simultaneouslywith the formation of the outer core 32.

[Advantage]

The composite material constituting at least a part of the magnetic core3 (herein, the outer core 32) satisfies a specific relative magneticpermeability so that a loss can be reduced. Therefore, the reactor 1 hasa low loss. Moreover, the composite material constituting at least apart of the magnetic core 3 (herein, the outer core 32) satisfies thespecific magnetic permeability. Consequently, the gap member or the airgap can be reduced (herein, they can be omitted). Accordingly, thereactor 1 has the small number of components, and an assembling step ora step of bonding the gap member can be reduced (herein, they can beomitted). Therefore, the productivity is also high.

Moreover, the reactor 1 has a high saturation magnetic flux density (0.6T or more) because the proportion of the magnetic component of thecomposite material constituting the outer core 32 is high (the contentof the magnetic powder is more than 50% by volume). In the reactor 1,particularly, the inner core 31 is made of the powder compact so thatthe inner core 31 also has a high saturation magnetic flux density. Inthe reactor 1, accordingly, the whole magnetic core 3 has a highersaturation magnetic flux density (a value obtained by averaging thesaturation magnetic flux density of the magnetic core 3) as comparedwith the case where the whole magnetic core 3 is constituted of thecomposite material.

Furthermore, the reactor 1 constitutes the outer core 32 with thecomposite material. Consequently, it is possible to obtain advantagesthat (1) the magnetic characteristic can easily be changed, (2) the coil2 and the inner core 31 are covered to enable their protection andmechanical protection from the external environment because the polymercomponent such as a resin is possessed, (3) the polymer component suchas the resin can be utilized for a bonding material to the inner core31, and (4) the reactor 1 can be formed simultaneously with theformation of the outer core 32 so that the productivity is high.

In addition, referring to the reactor 1, the saturation magnetic fluxdensity of the inner core 31 is higher than that of the outer core 32.Consequently, in the case where there is obtained the same magnetic fluxas that of a core constituted of a single material (a core having auniform saturation magnetic flux density as a whole), the sectional areaof the inner core 31 (particularly, a portion covered with the coil 2)can be reduced. By reducing the size of the inner core 31, it is alsopossible to reduce the size of the coil 2 (to shorten the wire 2 w).Moreover, the reactor 1 has a gapless structure. For this reason, it ispossible to reduce a copper loss caused by a magnetic flux leakage in agap portion. Therefore, the coil 2 and the inner core 31 can be disposedclose to each other. From the foregoing, the reactor 1 is small-sized.Moreover, it is possible to reduce the weight of the reactor 1 bydecreasing the size of the coil 2 (shortening the coil 2).

Second Embodiment

In the first embodiment, there is proposed the configuration in whichthe composite material forming a part of the magnetic core isconstituted of the magnetic powder and the polymeric material (theresin). In addition, in the case where at least a part of the magneticcore is constituted of the composite material, it is possible to employa configuration in which the composite material contains the nonmagneticpowder constituted of a material of at least one type, that is, aconfiguration in which the magnetic core is constituted of the compositematerial containing the magnetic powder, the nonmagnetic powder, and thepolymeric material. It is assumed that the “magnetic material” of themagnetic powder is a ferromagnetic material in a wide sense and istypically a soft magnetic material. It is assumed that the “nonmagneticmaterial” of the nonmagnetic powder is not the ferromagnetic material.

Nonmagnetic Powder

The nonmagnetic powder has an effect for suppressing the sedimentationof the magnetic powder in the manufacture of the composite material. Inorder to fully obtain the effect, it is preferable that the nonmagneticpowder should have a smaller specific gravity than the magnetic powder.More specifically, examples of the nonmagnetic powder include the metalsuch as Al, a non-metallic inorganic material such as ceramics orsilicon (Si), for example, SiO₂, Al₂O₃, Fe₂O₃, BN, AlN, ZnO or TiO₂, anorganic material such as a silicone resin, and the like. In particular,the SiO₂ (silica) can apply a thixotropic property to a resin, and caneasily suppress the sedimentation of the magnetic powder in the casewhere the polymeric material is set to be the resin. If the nonmagneticpowder constituted of a material having a high thermal conductivity, forexample, SiO₂, Al₂O₃, BN or AlN is contained, the heat-releaseperformance of the composite material can be enhanced. By utilizing thecomposite material, therefore, it is possible to obtain a magnetic coreor a reactor which is excellent in the heat-release performance. Ifpowder containing a silicone resin is contained, it is possible tosuppress generation of a crack on the composite material. By utilizingthe composite material, accordingly, it is possible to obtain a magneticcore or a reactor which has a high strength. In the case where asilicone resin is used for the polymeric material to be a binder, apowder silicon resin is added to an uncured silicone resin. It is alsopossible to employ a configuration in which nonmagnetic powderconstituted of a material of one type is contained and a configurationin which nonmagnetic powder constituted of different materials of pluraltypes is contained. In addition, referring to the configuration in whichthe nonmagnetic powder is contained, a nonmagnetic particle is presentedbetween magnetic particles so that the relative magnetic permeability ofthe composite material can also be reduced easily.

Examples of the shape of magnetic particles constituting the nonmagneticpowder include a spherical shape, a nonspherical shape (for example, aplate shape, a needle shape, a rod shape or the like) and the like. Ifthe spherical shape is taken, particularly, there is an advantage thatthe nonmagnetic powder can easily be filled in a clearance formedbetween the magnetic particles and fluidity is high. Moreover, thenonmagnetic particle may be a solid element or a hollow body. In thecase of the hollow body, it is possible to reduce the weight of thecomposite material. Commercially available powder can be utilized forthe nonmagnetic powder. It is possible to employ a configuration inwhich nonmagnetic powder having a shape of one type is included or aconfiguration in which nonmagnetic powder having different shapes ofplural types is included.

It is preferable that the magnetic powder and the nonmagnetic powder inthe composite material should have different particle diameters. Inparticular, there is preferred a configuration in which a maximumparticle diameter r_(n)max having a peak in the nonmagnetic powder issmaller than a minimum particle diameter r_(m)min having a peak in themagnetic powder when the particle size distribution of the mixed powderincluding the magnetic powder and the nonmagnetic powder is taken.Referring to this configuration, a magnetic particle having a largerparticle diameter than a nonmagnetic particle is present at a highfrequency. For this reason, a fine nonmagnetic particle can be presentin a clearance formed between the magnetic particles, it is possible toprevent the packing density of the magnetic powder from being reducedwith the inclusion of the nonmagnetic powder or the packing density canbe prevented from being substantially reduced. In other words, thisconfiguration can prevent a proportion of a magnetic component frombeing reduced due to the inclusion of the nonmagnetic powder.

As a difference between the particle diameters of the magnetic particleand the nonmagnetic particle is increased, the advantages can easily beobtained. Therefore, it is preferable that the maximum particle diameterr_(n)max having the peak in the nonmagnetic powder should be ⅓ or lessof the minimum particle diameter r_(m)min having the peak in themagnetic powder (r_(n)max≦(⅓)×r_(m)min) and/or the maximum particlediameter having the peak in the nonmagnetic powder should be 20 μm orless (r_(n)max≦20 μm). As the nonmagnetic powder is smaller, theclearance can be filled more efficiently, and preferably, thenonmagnetic powder can be interposed in only the clearance and caneasily spread uniformly around the magnetic particles. Therefore, thesedimentation of the magnetic particle can be suppressed effectively.Accordingly, r_(n)max≦(⅕)×r_(m)min and r_(n)max 10 μm is morepreferable. For example, it is possible to utilize nonmagnetic powderhaving a particle diameter which is in a range from approximately 1 μmto 10 μm or fine nonmagnetic powder having a particle diameter of lessthan 1 μm. Even if the nonmagnetic powder is thus fine, it can easily behandled and is excellent in workability. Examples of a specificconfiguration include a composite material in which particle diametersr₁ and r₂ of first and second peaks of the magnetic powder and aparticle diameter r_(n) having a peak of the nonmagnetic powder in theparticle size distribution of the mixed powder satisfy r₂=2r₁ andr_(n)=(⅓)×r₁. It is possible to employ any of a configuration containingnonmagnetic powder having a single particle diameter (that is, aconfiguration having a single peak of the nonmagnetic powder) and aconfiguration containing nonmagnetic powder having a plurality ofdifferent particle diameters (that is, a configuration in which aplurality of peaks of the nonmagnetic powder is present). In the lattercase, both the magnetic powder and the nonmagnetic powder have aplurality of peaks.

If the content of the nonmagnetic powder is 0.2% by mass or more withrespect to the whole composite material, the nonmagnetic particle fullyspreads around the magnetic powder so that the sedimentation of themagnetic powder can be suppressed effectively. In the case where thenonmagnetic powder is constituted of a material having a high thermalconductivity, the nonmagnetic powder is sufficiently present if thenonmagnetic powder of 0.2% by mass or more is contained. Therefore, theheat-release performance of the composite material can be enhanced moregreatly. In addition, the composite material can have uniformheat-release performance by the uniform presence of the nonmagneticpowder as described above. As the amount of the nonmagnetic powder islarger, the advantage can be obtained more greatly. Therefore, thecontent of the nonmagnetic powder (a total amount in the case whereplural types of materials are included) is preferably 0.3% by mass ormore, and is further preferably 0.5% by mass or more with respect to thewhole composite material. If the nonmagnetic powder is excessivelycontained, however, the proportion of the magnetic component is reduced.For this reason, the content of the nonmagnetic powder is preferably 20%by mass or less, is further preferably 15% by mass or less, and isparticularly preferably 10% by mass or less.

The composite material containing the nonmagnetic particle caneffectively prevent the sedimentation of the magnetic powder in amixture of raw materials in manufacture. Therefore, the mixture isexcellent in fluidity and can be filled well in a molding die (the case4 in the first embodiment). Accordingly, the composite material can bemanufactured highly precisely even when it has a complicated shape.Moreover, the magnetic particle can easily be dispersed uniformly intothe mixture and can be molded and hardened in the state where themagnetic powder is uniformly dispersed. Therefore, it is possible toobtain a composite material in which the magnetic powder and thenonmagnetic powder are uniformly dispersed. In other words, the portionwhere the magnetic powder is locally present to incur a high loss ishardly produced. As a result, it is possible to obtain the compositematerial in which the loss for the whole composite material can bereduced. Further, since the composite material in its entirety exhibitsthe uniform magnetic characteristic and the uniform thermalcharacteristic, the composite material is highly reliable.

[Test Example]

A composite material containing magnetic powder and a polymeric materialwas prepared and a magnetic characteristic of the composite materialthus obtained was examined

Pure iron powder (Fe: 99.5% by mass or more), Fe—Si alloy powder (Si:6.5% by mass, a residual part Fe and inevitable impurities) wereprepared as magnetic powder of a raw material. The pure iron powder wasset to be coating powder including insulating coating constituted ofphosphate on an outer periphery of a pure iron particle, and the Fe—Sialloy powder was set to be bare powder having no insulating coating.

A particle size distribution of each prepared magnetic powder wasexampled using a commercially available device (Microtrac particle sizedistribution analyzer MT3300, available from NIKKISO CO., LTD), whichemploys a laser diffraction and scattering method. The result (a mode:μm, a high frequency particle diameter: μm) is shown in Tables 1 and 2.A thickness of the insulating coating included in the coating powder isapproximately 0.1 μm or less, which is very thin. Therefore, theparticle diameter of the coating powder is not substantially influenced.For this reason, the particle diameter of the coating powder is treatedas the particle diameter of the magnetic powder.

By using a microscope observation image for a section of the preparedmagnetic powder, a degree of circularity (a maximum diameter/a circleequivalent diameter) was examined as described above (the number ofmeasured particles: 1000 or more). The result is also shown in Tables 1and 2.

There was obtained a density ratio=an apparent density/a true density ofthe prepared magnetic powder. The result is shown in Table 3. Theapparent density was obtained based on JIS Z 2504 (2000) “Metallicpowders—Determination of apparent density”. The apparent density of theprepared pure iron powder had fine powder (a mode of 54 μm): 3.4 g/cm³,coarse powder (a mode of 109 μm): 3.29 g/cm³, and fine/coarse mixedpowder: 3.62 g/cm³. The apparent density of the Fe—Si alloy powder hadfine powder (a mode of 11 μm): 2.82 g/cm³, coarse powder (a mode of 141μm): 3.25 g/cm³, and fine/coarse mixed powder: 3.34 g/cm³. The truedensity was obtained based on a composition and a specific gravity of aconstituent element. The true density of the pure iron powder and theFe—Si alloy powder simple substance is obtained by examining aliterature value or the like. In the case where powder made of aplurality of different materials is contained, moreover, a density ratiowas obtained for the mixed powder. For example, in the case where thepure powder and the Fe—Si alloy powder are contained, the density ratiowas obtained by carrying out calculation in accordance with (truedensity of iron×pure iron powder content (% by volume)+true density ofFe—Si alloy×Fe—Si alloy powder content (% by volume)×100.

For all samples, an epoxy resin was prepared as a polymeric material ofa raw material. A composite material containing a nonmagnetic powder wasalso prepared. A silica filler (a particle diameter was 5 nm or more andis 50 nm or less, a mode of 12 nm 20 μm) was prepared for thenonmagnetic powder. The nonmagnetic powder was prepared such that acontent with respect to the whole composite material is 0.3% by mass0.2% by mass). The presence of the inclusion of the nonmagnetic powderis also shown in Table 3.

Magnetic powder, a polymeric material and nonmagnetic powder (properly)were prepared such that the content of the magnetic powder with respectto the whole composite material is equal to the amounts (% by volume)shown in Tables 1 and 2 and it is possible to obtain a compositematerial having a size to enable sufficient preparation of a samplewhich will be described later. A residual part except for the magneticpowder was a polymeric material and nonmagnetic powder (properly).

Although Tables 1 to 3 are shown in three tables for convenience of thesizes of the respective tables, sample conditions of sample No. 1-1 toNo. 1-10 are indicated in these three tables. For example, as themagnetic powder, the sample No. 1-1 includes only the pure iron powder,the sample No. 1-5 includes only the Fe—Si alloy powder, and the sampleNo. 1-9 includes both the pure iron powder and the Fe—Si alloy powder.

TABLE 1 Pure iron powder Fine Coarse High Content High Content SampleMode frequency Degree of (% by Mode frequency Degree of (% by No. (μm)(μm) circularity volume) (μm) (μm) circularity volume) 1-1 54 48-57 1.512 109 90-128 1.5 50 1-2 54 48-57 1.5 56 — — — — 1-3 — — — — 109 90-1281.5 56 1-4 54 48-57 1.5 12 109 90-128 1.5 48 1-5 — — — — — — — — 1-6 — —— — — — — — 1-7 — — — — — — — — 1-8 — — — — — — — — 1-9 — — — — 10990-128 1.5 56  1-10 — — — — 109 90-128 1.5 52

TABLE 2 Fe—Si alloy powder Fine Coarse High Content High Content SampleMode frequency Degree of (% by Mode frequency Degree of (% by No. (μm)(μm) circularity volume) (μm) (μm) circularity volume) 1-1 — — — — — — —— 1-2 — — — — — — — — 1-3 — — — — — — — — 1-4 — — — — — — — — 1-5 118-17 1.3 12 141 125-176 1.1 50 1-6 11 8-17 1.3 56 — — — — 1-7 — — — —141 125-176 1.1 56 1-8 11 8-17 1.3 12 141 125-176 1.1 48 1-9 11 8-17 1.314 — — — —  1-10 11 8-17 1.3 13 — — — —

TABLE 3 Sample Nonmagnetic Density No. powder ratio 1-1 No 0.46 1-2 No0.43 1-3 No 0.42 1-4 Yes 0.46 1-5 No 0.45 1-6 No 0.38 1-7 No 0.44 1-8Yes 0.45 1-9 No 0.47  1-10 Yes 0.47

The magnetic powder, the polymeric material (a resin) and thenonmagnetic powder (properly) which were prepared were mixed to make amixture, the mixture was filled in a molding die having a predeterminedshape, and the resin was then cured to obtain a composite material.Herein, a disc-shaped sample having an outside diameter: φ34 mm, aninside diameter: (φ20 mm and a thickness: 5 mm was made as a sample formeasuring a magnetic characteristic, and a disk-shaped sample having adiameter: φ50 mm and a thickness: 5 mm was made as a sample formeasuring heat-release performance.

For each of the composite materials thus obtained, a saturation magneticflux density (T), a relative magnetic permeability μ and an iron loss(W/cm³) were measured. These results are shown in Table 4.

The saturation magnetic flux density is set to be a magnetic fluxdensity obtained when a magnetic field of 10000(Oe) (=795.8 kA/m) isapplied to a ring-shaped composite material by means of an electromagnetand magnetic saturation is fully carried out.

The relative magnetic permeability was measured in the following manner.Wires having a primary side: 300 turns and a secondary side: 20 turnswere applied to the ring-shaped composite material of each sample, a B-Hinitial magnetization curve was measured in a range of H=0 (0e) to 100(0e), a maximum value of B/H of the B-H initial magnetization curve wasobtained, and the maximum value was set to be the relative magneticpermeability μ. Herein, the magnetization curve is a so-called directcurrent magnetization curve.

The iron loss was calculated as follows. A hysteresis loss Wh (W/cm³)and an eddy current loss We (W/cm³) at an excitation magnetic fluxdensity Bm: 1 kG (=0.1 T) and a measuring frequency: 10 kHz weremeasured by using a BH curve tracer for the ring-shaped compositematerial of each sample, and the hysteresis loss Wh+the eddy currentloss We was calculated as the iron loss (W/cm³).

The resin component was removed to extract the magnetic powder from theobtained composite material, and particle size analysis of the obtainedmagnetic powder was carried out by the laser diffraction and scatteringmethod in the same manner as described above. Consequently, a point fora particle size having a mode shown in Tables 1 and 2 had a peak in ahistogram. The sample No. 1-1, No. 1-4, No. 1-5, and No. 1-8 to No. 1-10had a plurality of peaks. In the composite material containing thenonmagnetic powder, the nonmagnetic powder had a minimum particle sizehaving a peak in the particle size distribution. Moreover, the densityratio of the magnetic powder extracted from the obtained compositematerial was found in the same manner as described above. Consequently,the density ratio was substantially equal to the value shown in Tables 1and 2. Accordingly, the magnetic powder in the composite material madein this test substantially maintains the particle size distribution andthe density ratio of the powder used for the raw material.

TABLE 4 Sample Saturation Magnetic Relative Magnetic Iron Loss No. FluxDensity (T) Permeability μ (W 1/10k) (W/cm³) 1-1 1.25 29 497 1-2 1.17 17460 1-3 1.17 18 472 1-4 1.22 24 462 1-5 1.1 28 185 1-6 1.05 16 165 1-71.05 17 173 1-8 1.08 22 170 1-9 1.28 33 432  1-10 1.24 30 393

As shown in Table 4, the samples having the magnetic powder constitutedof the same material are compared with each other (comparison of thesamples No. 1-1, No. 1-2, No. 1-3 and No. 1-4 or comparison of No. 1-5,No. 1-6, No. 1-7 and No. 1-8). A composite material having a relativemagnetic permeability which is more than 20 and 35 or less has a highersaturation magnetic flux density as compared with the composite materialwhich does not satisfy the relative magnetic permeability of more than20 and 35 or less. In general, there is a tendency that the iron loss isincreased with an increase in the saturation magnetic flux density whenthe saturation magnetic flux density is enhanced. However, in the samplehaving the relative magnetic permeability which is more than 20 and 35or less, the iron loss associated with the increase in the saturationmagnetic flux density is rarely increased or can be made comparativelysmall.

As shown in Table 4, moreover, it is found that the composite materialincluding the magnetic powder of which particle size distribution has aplurality of peaks (the samples No. 1-1, No. 1-4, No. 1-5, No. 1-8, No.1-9, No. 1-10) can easily have a relative magnetic permeability of morethan 20 as compared with the composite material including the magneticpowder having a single peak (the samples No. 1-2, No. 1-3, No. 1-6, No.1-7). Furthermore, as compared with the samples having the magneticpowder formed of the same material (comparison of the samples No. 1-1,No. 1-2, No. 1-3 and No. 1-4 or comparison of No. 1-5, No. 1-6, No. 1-7and No. 1-8), the composite material including the magnetic powder ofwhich particle size distribution has a plurality of peaks has a highersaturation magnetic flux density as compared with the composite materialincluding the magnetic powder having a single peak (that is, a compositematerial including only one of the fine magnetic powder or the coarsemagnetic powder). Moreover, it is found that the iron loss associatedwith an increase in the saturation magnetic flux density is rarelyincreased or can be made comparatively small in the composite materialincluding the magnetic powder of which particle size distribution has aplurality of peaks. In addition, the saturation magnetic flux density ofthe composite material including the magnetic powder of which particlesize distribution has a plurality of peaks (that is, powder includingboth the fine magnetic powder and the coarse magnetic powder) is greaterthan a value expected from an interpolation of the saturation magneticflux density of the composite material including only the fine magneticpowder and the saturation magnetic flux density of the compositematerial including only the coarse magnetic powder. The reason why theresult is obtained is unknown. By mixing both the fine magnetic powderand the coarse magnetic powder, however, it is supposed that ademagnetizing coefficient might be changed. Moreover, the reason why thecomposite material including the magnetic powder of which particle sizedistribution has a plurality of peaks has a low loss is supposed asfollows. In other words, the fine magnetic powder is present at a highfrequency so that an eddy current loss is reduced.

In addition, from the test, it is found that the saturation magneticflux density is high when the pure iron powder is used, and the low lossis obtained without an insulating coating when the iron alloy is used.Moreover, it is found that a smaller particle size tends to have a lowerloss regardless of the material from the comparison between “the samplesNo. 1-2 and No. 1-3” and between “the samples No. 1-6 and No. 1-7”, forexample.

Furthermore, it is found that the composite material containing thenonmagnetic powder has a lower loss from comparison between “the samplesNo. 1-1 and No. 1-4”, between “the samples No. 1-5 and No. 1-8” andbetween “the samples No. 1-9 and No. 1-10”, for example. The reason issupposed as follows. In other words, the magnetic powder and thenonmagnetic powder are uniformly present in the composite material, anda portion where more magnetic powder is locally present is not presentsubstantially. Furthermore, it is found that the relative magneticpermeability is lower. The reason is supposed as follows. Morespecifically, the nonmagnetic particle is interposed between themagnetic particles in the composite material.

Referring to the prepared disk-shaped composite material, a thermalconductivity was measured by a temperature inclination method.Consequently, the thermal conductivity of the composite materialincluding the fine/coarse mixed magnetic powder was higher than amaximum value in the case where only one of the fine magnetic powder andthe coarse magnetic powder is used, and furthermore, was higher than avalue expected from the interpolation. The reason is supposed asfollows. More specifically, the fine magnetic particle is interposedbetween the coarse magnetic particles to form a continuous heatconducting path.

Third Embodiment

In the first embodiment, there is employed the configuration in whichonly a part of the magnetic core is constituted of the specificcomposite material. In addition, it is possible to employ aconfiguration in which all of the magnetic cores are constituted of thespecific composite material, that is, a configuration in which amagnetic core constituted of the composite material according to thepresent invention is present on an inside and outside of a coil 2.

As a specific configuration, for example, a magnetic characteristic of awhole magnetic core is uniform. In other words, a saturation magneticflux density of the whole magnetic core is 0.6 T or more (preferably 1.0T or more) and a relative magnetic permeability is more than 20 and 35or less (preferably is more than 20 and 30 or less), a content of themagnetic powder is more than 50% by volume and 75% by volume or less,and the same values are taken in optional portions of the magnetic core.Referring to this configuration, the relative magnetic permeability ofthe whole magnetic core is sufficiently low (35 or less at a maximum).Therefore, a gap member can be reduced more greatly, and preferably, agapless structure can be employed. Accordingly, in this configuration,it is possible to further reduce the number of components and todecrease a size and a weight. In the case of the gapless structure, fluxleakage from gap portions is not caused and an increase in the size ofthe reactor due to the presence of gaps can also be suppressed.

It is possible to manufacture the magnetic core according to thisconfiguration by using the case 4 described in the first embodiment as amolding die, accommodating the coil 2 in a proper position of the case4, then filling the case 4 with a mixture containing the magnetic powderand a polymeric material such as a resin, which are raw materials andcuring the polymeric material such as a resin, for example. Referring tothis configuration, the inner core and the outer core described in thefirst embodiment can be molded at the same time, and furthermore, theirassembling and bonding steps or the like are not required so thatproductivity is high. According to this configuration, moreover, thecase 4 is used as the molding die. Consequently, it is possible toeasily form the magnetic core 3 regardless of a complicated shape. Alsoin this respect, the productivity is high. In a configuration in whichthe inside and the outside of the coil are covered with a compositematerial, furthermore, a coil can be protected by the polymericcomponent of the composite material. An external shape of the outer coretypically conforms to an inner peripheral shape of the case 4.

Alternatively, the columnar compacts are fabricated by the specificcomposite material and the magnetic core can be built by utilizing atleast one of the columnar compacts. For example, the inner coredescribed in the first embodiment is set to be the columnar compactfabricated by the specific composite material, and the outer core can bemanufactured by filling the case 4 with the mixture of the raw materialsas described above. In this configuration, their assembling and bondingsteps or the like of the inner core and the outer core are not requiredso that productivity is high. According to this configuration, moreover,the case 4 is used as the molding die. Consequently, it is possible toeasily form the magnetic core (particularly, the outer core) regardlessof a complicated shape. Also in this respect, the productivity is high.In a configuration in which the outside of the coil is covered with acomposite material, furthermore, a coil can be protected by thepolymeric component of the composite material. An external shape of theouter core typically conforms to an inner peripheral shape of the case4.

Alternatively, it is possible to employ a configuration in which boththe inner core and the outer core are used as the columnar compactsconstituted of the specific composite material and these columnarcompacts are assembled to form a magnetic core. Referring to thisconfiguration, a gap member can be omitted or a case can be omitted.Accordingly, it is possible to reduce the number of components and todecrease a size and a weight. According to this configuration, moreover,it is sufficient that a mixture of one type is used for manufacturingthe columnar compact. Therefore, preparation is easily carried out andproductivity is high.

In all cases, it is possible to employ a configuration in which amagnetic characteristic of the magnetic core is partially varied byregulation of a material, a shape, a size, a content or the like of themagnetic powder. Referring to this configuration, in the case where thematerial of the magnetic powder is identical, the magneticcharacteristic can easily be changed by the regulation of the content sothat a composite material having a desirable characteristic can readilybe manufactured. For example, it is possible to easily obtain acomposite material having a high saturation magnetic flux density and ahigh relative magnetic permeability when a blending amount of themagnetic powder is increased, and it is possible to easily obtain acomposite material having a low saturation magnetic flux density and alow relative magnetic permeability when the blending amount of themagnetic powder is decreased. A configuration in which the magneticcharacteristic of the magnetic core is partially varied can easily bebuilt through utilization of the columnar compact formed of at least onecomposite material described above and the composite material molded byusing the case or utilization of only the columnar compact formed of aplurality of composite materials.

For example, the saturation magnetic flux density and the relativemagnetic permeability in the composite material constituting the innercore can be caused to be higher than the saturation magnetic fluxdensity and the relative magnetic permeability in the composite materialconstituting the outer core in the same manner as in the firstembodiment through the regulation of the material, the content or thelike of the magnetic powder. In this case, it is possible to reduce thesize as described above. Alternatively, the saturation magnetic fluxdensity and the relative magnetic permeability in the composite materialconstituting the outer core can be caused to be higher than thesaturation magnetic flux density and the relative magnetic permeabilityin the composite material constituting the inner core. In this case, itis possible to reduce the leakage flux from the outer core to anoutside, thereby decreasing a loss. In the case where the whole magneticcore is constituted of the composite material, thus, it is possible toeasily vary the magnetic characteristics of the magnetic core partiallyby building at least a part of the magnetic core through the compactconstituted of the composite material.

Fourth Embodiment

Contrary to the structure according to the first embodiment, it ispossible to employ a configuration in which at least a part of a portiondisposed on an inside of a tube-shaped coil formed by winding a wire ina magnetic core is constituted of the specific composite material and atleast a part of a portion disposed on an outside of the coil isconstituted of a powder compact. For example, a columnar compactconstituted of the specific composite material (a content of magneticpowder: more than 50% by volume and 75% by volume or less, a saturationmagnetic flux density: 0.6 T or more, preferably 1.0 T or more), arelative magnetic permeability: more than 20 and 35 or less, preferablymore than 20 and 30 or less) is fabricated and is set to be an innercore, and an outer core is constituted of a powder compact. For example,the outer core includes a tube-shaped member disposed on an outerperiphery of a coil and a plate-shaped member disposed on an each endsurface of the coil. By combining the compact and the powder compactwhich are constituted of the composite material, it is possible to builda magnetic core. The magnetic core can have a configuration in which therelative magnetic permeability of the inner core including a polymericcomponent such as a resin is lower than that of the outer core, and thesaturation magnetic flux density of the outer core constituted of thepowder compact is higher than that of the inner core. By this structure,it is possible to reduce a leakage of a magnetic flux from the outercore to the outside, thereby decreasing a loss.

Fifth Embodiment

Although the vertical type configuration has been employed in the firstembodiment, it is possible to employ a configuration (hereinafterreferred to as a horizon type) in which a coil 2 is accommodated in acase 4 such that an axial direction of the coil is parallel with abottom surface of the case 4. Referring to the horizontal configuration,a distance from an outer peripheral surface of the coil 2 to the bottomsurface of the case 4 is shorted so that heat-release performance can beenhanced.

Sixth Embodiment

Although the configuration in which the single coil is provided has beenemployed in the first embodiment, it is possible to employ aconfiguration in which a coil 2 having a pair of coil elements 2 a and 2b which are formed by spirally winding a single continuous wire 2 w asin a reactor 15 shown in FIG. 3(A) and an annular-shaped magnetic core 3where these coil elements 2 a and 2 b are disposed (FIG. 3(B)) areprovided.

The coil 2 typically takes a configuration in which both of the coilelements 2 a and 2 b are horizontally disposed side by side such thatthe axial directions of the respective coil elements 2 a and 2 b areparallel with each other, and are coupled to each other through acoupling portion 2 r formed by folding back a part of the wire 2 w.Examples of the other coil include a configuration in which therespective coil elements 2 a and 2 b are separately formed by means oftwo different wires, and ends of the wires constituting the respectivecoil elements 2 a and 2 b are bonded and integrated by welding, pressurebonding, soldering or the like. The coil elements 2 a and 2 b are formedinto a hollow tube shape with the same winding number in the samewinding direction.

The magnetic core 3 has a pair of columnar inner cores 31 and 31disposed respectively at the inside of the respective coil elements 2 aand 2 b and a pair of columnar outer cores 32 and 32 disposed on theoutside of the coil 2 and exposed from the coil 2. End surfaces of bothof the inner cores 31 and 31 disposed apart from each other are coupledto each other through one of the outer cores 32 and the other endsurfaces of both of the inner cores 31 and 31 are coupled to each otherthrough the other outer core 32 as shown in FIG. 3(B) so that themagnetic core 3 is formed into an annular shape.

In addition, the reactor 15 includes an insulator 5 for enhancinginsulation performance between the coil 2 and the magnetic core 3. Theinsulator 5 includes a pair of tube-shaped portions (not shown) disposedon the outer peripheries of the columnar inner cores 31 and 31 and apair of frame plate portions 52 abutting on the end surface of the coil2 (a surface where a turn is seen like an annular shape) and having twothrough holes (not shown) where the inner cores 31 and 31 are inserted.For a constituting material of the insulator 5, it is possible toutilize an insulating material such as a PPS resin, a PTFE resin or LCP.It is also possible to employ a configuration in which the insulator 5is not provided.

Referring to the reactor 15 including the coil elements 2 a and 2 b, atleast a part of the magnetic core 3 is constituted of a specificcomposite material. More specifically, the composite material satisfiesa content of magnetic powder: more than 50% by volume and 75% by volumeor less, a saturation magnetic flux density: 0.6 T or more, preferably1.0 T or more, a relative magnetic permeability: more than 20 and 35 orless, and preferably more than 20 and 30 or less.

As a specific configuration of the magnetic core 3, for example, it ispossible to employ a configuration in which the composite material and amagnetic material in the other configuration (a lamination product of apowder compact and an electromagnetic steel sheet) (that is, aconfiguration in which a part of the magnetic core is constituted of thecomposite material according to the present invention) as described inthe first embodiment. This configuration can easily vary the magneticcharacteristics of the magnetic core partially in the same manner as inthe first embodiment.

For example, it is possible to employ a configuration in which the innercores 31 and 31 to be inserted into the coil elements 2 a and 2 brespectively are constituted of a powder compact and the outer cores 32and 32 are constituted of a columnar compact formed of the specificcomposite material. Referring to this configuration, it is possible tobuild the annular-shaped magnetic core 3 by assembling the powdercompact and the columnar compact formed of the composite material. Inthis configuration, a gap member can be omitted or a case can beomitted. Accordingly, it is possible to reduce the number of componentsand to decrease a size and a weight. In this configuration, thesaturation magnetic flux density and the relative magnetic permeabilityof the inner core 31 are higher than the saturation magnetic fluxdensity and the relative magnetic permeability of the outer core 32.

As another configuration, it is possible to employ a configuration inwhich the assembly of the coil elements 2 a and 2 b and the powdercompact are covered with the specific composite material as in the firstembodiment. In this configuration, a case (not shown) is used as amolding die and the assembly of the coil 2 and the inner cores 31 and 31is accommodated in the case, the case is then filled with a mixture tobe a raw material, and a polymeric material such as a resin is cured sothat the composite material can be manufactured (at this time, thereactor 15 can also be manufactured) in the same manner as in the firstembodiment. The composite material is molded to couple the inner cores31 and 31 and builds the outer core 32. Therefore, their assembling andbonding steps or the like are not required so that productivity is high.By using the case as the molding die, moreover, the composite materialcan easily form the magnetic core regardless of a complicated shape.Also in this respect, the productivity is high. In a configuration inwhich the outside of the coil is covered with the composite material,furthermore, a coil can be protected by the polymeric component of thecomposite material. An external shape of the outer core typicallyconforms to an inner peripheral shape of the case.

In these configurations, the saturation magnetic flux densities of theinner cores 31 and 31 constituted of the powder compact to be insertedinto the coil elements 2 a and 2 b are higher than those of the outercores 32 and 32 constituted of the composite material containing thepolymeric material such as a resin as described above. Therefore, it ispossible to reduce a size of the inner core 31. Accordingly, thisconfiguration can reduce (1) a size of the reactor, (2) a weight of thereactor by shortening the wire 2 w, and the like.

Alternatively, it is possible to take a configuration in which the innercores 31 and 31 to be inserted into the coil elements 2 a and 2 brespectively are constituted of the columnar compacts formed of thespecific composite material and the outer cores 32 and 32 areconstituted of the powder compact. This configuration can build theannular-shaped magnetic core 3 by assembling the columnar compactconstituted of the composite material and the powder compact.

In the configuration, the relative magnetic permeability of the innercore 31 containing the polymeric component such as a resin is lower thanthe relative magnetic permeability of the outer core 32 disposed on theoutside of the coil elements 2 a and 2 b, and the saturation magneticflux density of the outer core 32 formed of the powder compact is higherthan the saturation magnetic flux density of the inner core 31. By thisstructure, a leakage of a magnetic flux from the outer core 32 to theoutside can be reduced so that a loss can be reduced.

In the case where a part of the magnetic core 3 is provided with amagnetic material having a high relative magnetic permeability, forexample, a powder compact or a lamination product of electromagneticsteel sheets, a gap material constituted of a material having a lowermagnetic permeability than a core piece 31 m (typically, a nonmagneticmaterial such as alumina) is permitted to be provided between the corepieces 31 m formed of the powder compact, the composite material or thelike or in the middle of the individual core pieces 31 m in order toregulate an inductance. In the example shown in FIG. 3(B), both theinner core 31 and the outer core 32 are set to be only the core piece 31m. For the gap material, it is also possible to use a nonmagneticmaterial as well as a magnetic material having a relative magneticpermeability which is 1.05 or more and 2 or less. Examples of themagnetic material include a mixture including a nonmagnetic materialsuch as a polyphenylene sulfide (PPS) resin and a magnetic material suchas iron powder, and the like.

As described in the third embodiment, alternatively, it is possible toemploy a configuration in which all of the magnetic cores 3 disposed onthe inside and the outside of the coil elements 2 a and 2 b areconstituted of the specific composite material. The magnetic core 3according to this configuration satisfies a content of magnetic powder:more than 50% by volume and 75% by volume or less, a saturation magneticflux density: 0.6 T or more, preferably, 1.0 T or more, a specificmagnetic permeability: more than 20 and 35 or less, and preferably morethan 20 and 35 or less in an optional portion. In other words, both theinner core 31 and the outer core 32 have the contents, the saturationmagnetic flux densities and the relative magnetic permeabilities whichsatisfy specific ranges. In this configuration, the whole magnetic core3 has a relative magnetic permeability which is 35 or less. In thisconfiguration, therefore, a gap member can be reduced more greatly, andpreferably, a gapless structure can be employed, the number ofcomponents can further be reduced and a size and a weight can bedecreased. In the case of a gapless structure, flux leakage from gapportions is not caused and an increase in the size of the reactor due tothe presence of gaps can also be suppressed.

As a more specific configuration, it is possible to employ aconfiguration in which the material of the whole magnetic core 3 isuniform. This configuration can be manufactured by using a case (notshown) as a molding die, accommodating the coil 2 in a proper positionof the case, then filling the case with a mixture to be a raw materialand curing a polymeric material such as a resin, for example. Referringto this configuration, the inner core 31 and the outer core 32 can bemolded at the same time, and furthermore, their assembling and bondingsteps or the like are not required so that productivity is high.According to this configuration, moreover, the case is used as themolding die. Consequently, it is possible to easily form the magneticcore 3 regardless of a complicated shape. Also in this respect, theproductivity is high. In a configuration in which the inside and theoutside of the coil are covered with a composite material, furthermore,a coil can be protected by the polymeric component of the compositematerial. An external shape of the outer core typically conforms to aninner peripheral shape of the case.

As described in the third embodiment, alternatively, it is possible tofabricate columnar compacts by the specific composite material and tobuild the magnetic core 3 by utilizing at least one of the columnarcompacts. For example, the inner cores 31 and 31 are set to be thecolumnar compacts fabricated by the specific composite material, and theouter core can be manufactured by using the case (not shown) as amolding die, and filling the case with the mixture of the raw materialsas described above. The outer core is molded to couple the inner cores31 and 31. For this reason, their assembling and bonding steps or thelike are not required so that productivity is high. The case is used asthe molding die. Consequently, it is possible to easily form themagnetic core 3 (particularly, the outer core 32) regardless of acomplicated shape. Also in this respect, the productivity is high. In aconfiguration in which the outside of the coil is covered with acomposite material, furthermore, a coil can be protected by thepolymeric component of the composite material. An external shape of theouter core typically conforms to an inner peripheral shape of the case.

Alternatively, it is possible to employ a configuration in which boththe inner cores 31 and 31 and the outer cores 32 and 32 are used as thecolumnar compacts constituted of the specific composite material andthese columnar compacts are assembled to form the magnetic core 3.Referring to this configuration, a gap member can be omitted or a casecan be omitted. Accordingly, it is possible to reduce the number ofcomponents and to decrease a size and a weight. According to thisconfiguration, moreover, it is sufficient that a mixture of one type isused for manufacturing the columnar compact. Therefore, preparation iseasily carried out and productivity is high.

As another configuration, it is possible to employ a configuration inwhich a magnetic characteristic of the magnetic core 3 is partiallyvaried by regulation of a material, a shape, a size, a content or thelike of the magnetic powder as described in the third embodiment.Referring to this configuration, in the case where the material of themagnetic powder is identical, the magnetic characteristic can easily bechanged by the regulation of the content so that a composite materialhaving a desirable characteristic can readily be manufactured. Forexample, it is possible to easily obtain a composite material having ahigh saturation magnetic flux density and a high relative magneticpermeability when a blending amount of the magnetic powder is increased,and it is possible to easily obtain a composite material having a lowsaturation magnetic flux density and a low relative magneticpermeability when the blending amount of the magnetic powder isdecreased. As described above, it is possible to easily build thisconfiguration through utilization of the columnar compact formed of atleast one composite material and the composite material molded by usingthe case or utilization of only the columnar compact formed of aplurality of composite materials.

For example, the saturation magnetic flux density and the relativemagnetic permeability in the composite material constituting the innercores 31 and 31 can be made higher than the saturation magnetic fluxdensity and the relative magnetic permeability in the composite materialconstituting the outer cores 32 and 32 through the regulation of thematerial, the content or the like of the magnetic powder. Accordingly,the size of the inner core can be reduced. Therefore, a size reductioncan be achieved. Alternatively, the saturation magnetic flux density andthe relative magnetic permeability in the composite materialconstituting the outer cores 32 and 32 can be made than the saturationmagnetic flux density and the relative magnetic permeability in thecomposite material constituting the inner cores 31 and 31. In this case,it is possible to reduce the leakage of the magnetic flux from the outercore to an outside, thereby decreasing a loss.

Seventh Embodiment

The reactor according to the first to sixth embodiments may be used fora component of a converter mounted on a vehicle or the like, or acomponent of a power conversion device including the converter.

For example, as shown in FIG. 4, a vehicle 1200, which is a hybridelectric vehicle or an electric vehicle, includes a main battery 1210, apower conversion device 1100 connected to the main battery 1210, and amotor (a load) 1220 driven by power fed from the main battery 1210 andused for traveling. The motor 1220 is typically a three-phasealternating current motor. The motor 1220 drives wheels 1250 duringtraveling and functions as a generator during regeneration. In case of ahybrid electric vehicle, the vehicle 1200 includes an engine in additionto the motor 1220. FIG. 4 illustrates an inlet as a charging portion ofthe vehicle 1200; however, a plug may be included.

The power conversion device 1100 includes a converter 1110 connected tothe main battery 1210, and an inverter 1120 that is connected to theconverter 1110 and performs conversion between direct current andalternating current. During traveling of the vehicle 1200, the converter1110 steps up a direct-current voltage (input voltage) of the mainbattery 1210, which is in a range from about 200 to 300 V, to a level ina range from about 400 to 700 V, and then feeds the power to theinverter 1120. Also, during regeneration, the converter 1110 steps downthe direct-current voltage (the input voltage) output from the motor1220 through the inverter 1120 to a direct-current voltage suitable forthe main battery 1210, and then uses the direct-current voltage for thecharge of the main battery 1210. During traveling of the vehicle 1200,the inverter 1120 converts the direct current stepped up by theconverter 1110 into predetermined alternating current and feeds thealternating current to the motor 1220. During regeneration, the inverter1120 converts the alternating current output from the motor 1220 intodirect current and outputs the direct current to the converter 1110.

As shown in FIG. 5, the converter 1110 includes a plurality of switchingelements 1111, a driving circuit 1112 that controls operations of theswitching elements 1111, and a reactor L. The converter 1110 convertsthe input voltage (in this situation, performs step up and down) byrepetition of on and off operations (switching operations). Theswitching elements 1111 each use a power device, such as field effecttransistor (FET) or an insulated-gate bipolar transistor (IGBT). Thereactor L uses a characteristic of a coil that disturbs a change ofcurrent which flows through the circuit, and hence has a function ofmaking the change smooth when the current is increased or decreased bythe switching operation. The reactor L is the reactor according to thefirst to sixth embodiments. The number of components is small so that aloss can be reduced. By including the reactor 1 and the like, the powerconversion device 1100 and the converter 1110 are excellent inproductivity and have a low loss.

The vehicle 1200 includes, in addition to the converter 1110, a feedingdevice converter 1150 connected to the main battery 1210, and anauxiliary power supply converter 1160 that is connected to a sub-battery1230 serving as a power source of an auxiliary 1240 and the main battery1210 and that converts a high voltage of the main battery 1210 to a lowvoltage. The converter 1110 typically performs DC-DC conversion, whereasthe feeding device converter 1150 and the auxiliary power supplyconverter 1160 perform AC-DC conversion. The feeding device converter1150 may include a kind that performs DC-DC conversion. The feedingdevice converter 1150 and the auxiliary power supply converter 1160 eachmay include a configuration similar to the reactor according to thefirst to sixth embodiments, and the size and shape of the reactor may beproperly changed. Also, the reactor according to the first to sixthembodiments may be used for a converter that performs conversion for theinput power and that performs only stepping up or stepping down.

The present invention is not limited to the above-described embodiments,and may be properly modified without departing from the scope of theinvention. For example, the composite material according to the presentinvention can be utilized in a core for a motor.

INDUSTRIAL APPLICABILITY

The composite material according to the present invention can beutilized for a material constituting a magnetic core to be used for amagnetic part including a coil, for example, a reactor, a motor or thelike. The reactor according to the present invention can be utilized fora component of a power conversion device such as a bidirectional DC-DCconverter or a converter of an air conditioner which is mounted on avehicle such as a hybrid electric vehicle, a plug-in hybrid electricvehicle, an electric vehicle or a fuel cell vehicle.

REFERENCE SIGNS LIST

-   -   1, 15: REACTOR    -   2: COIL    -   2 w: WIRE    -   2 a, 2 b: COIL ELEMENT    -   2 r: COUPLING PORTION    -   3: MAGNETIC CORE    -   31: INNER CORE    -   31 m: CORE PIECE    -   32: OUTER CORE    -   4: CASE    -   41: MOUNT PORTION    -   5: INSULATOR    -   52: FRAME PLATE PORTION    -   1100: POWER CONVERSION DEVICE    -   1110: CONVERTER    -   1111: SWITCHING ELEMENT    -   1112: DRIVING CIRCUIT    -   L: REACTOR    -   1120: INVERTER    -   1150: FEEDING DEVICE CONVERTER    -   1160: AUXILIARY POWER SUPPLY CONVERTER    -   1200: VEHICLE    -   1210: MAIN BATTERY    -   1220: MOTOR    -   1230: SUB-BATTERY    -   1240: AUXILIARY    -   1250: WHEEL

1. A composite material comprising magnetic powder and a polymeric material including the powder in a dispersion state, wherein a content of the magnetic powder with respect to the whole composite material is more than 50% by volume and 75% by volume or less, a saturation magnetic flux density of the composite material is 0.6 T or more, and a relative magnetic permeability of the composite material is more than 20 and 35 or less.
 2. The composite material according to claim 1, wherein a density ratio of the magnetic powder is 0.38 or more and 0.65 or less, and the density ratio is set to be an apparent density/a true density.
 3. The composite material according to claim 1, wherein the magnetic powder includes a plurality of particles constituted of the same material.
 4. The composite material according to claim 3, wherein the magnetic powder is iron powder, and an apparent density of the iron powder is 3.0 g/cm³ or more and 5.0 g/cm³ or less.
 5. The composite material according to claim 1, wherein the magnetic powder contains powder constituted of a plurality of materials having different relative magnetic permeabilities from each other.
 6. The composite material according to claim 1, wherein a plurality of peaks is present when a particle size distribution of the magnetic powder is taken.
 7. The composite material according to claim 1, wherein a degree of circularity of the particle constituting the magnetic powder is 1.0 or more and 2.0 or less.
 8. A reactor comprising a coil and a magnetic core, wherein at least a part of the magnetic core is constituted of the composite material according to claim
 1. 9. A reactor comprising a coil and a magnetic core, wherein the whole magnetic core is constituted of the composite material according to claim
 1. 10. A converter comprising the reactor according to claim
 8. 11. A power conversion device comprising the converter according to claim
 10. 12. A converter comprising the reactor according to claim
 9. 13. A power conversion device comprising the converter according to claim
 12. 